Technical Report ECSTR-IAM03-005 (ISBN: 0854 32798 3)
School of Electronics and Computer Science, University of Southampton

Evaluating Citebase, an open access Web-based citation-ranked search and impact discovery service

Steve Hitchcock, Arouna Woukeu, Tim Brody, Les Carr, Wendy Hall and Stevan Harnad

Open Citation Project, IAM Group, Department of Electronics and Computer Science, University of Southampton, SO17 1BJ, United Kingdom
Contact for correspondence: Steve Hitchcock

Version history of this report
For a printable version of this paper, and for a version history and links to earlier and later versions, see this cover page


Citebase is a new citation-ranked search and impact discovery service that measures citations of scholarly research papers which are openly accessible on the Web, i.e. papers that are assessable continuously online. Other services, such as ResearchIndex, have emerged in recent years to offer citation indexing of Web research papers. In the first detailed user evaluation of an open access Web citation indexing service, Citebase has been evaluated by nearly 200 users from different backgrounds. The paper details the procedures used in the evaluation, and analyses the results of this study, which took place between June and October 2002. It was found that within the scope of its primary components, the search interface and services available from its rich bibliographic records, Citebase can be used simply and reliably for the purpose intended, and that it compares favourably with other bibliographic services. It is shown tasks can be accomplished efficiently with Citebase regardless of the background of the user. More data need to be collected and the process refined before it is as reliable for measuring citation impact of indexed papers. Better explanations and guidance are required for first-time users. Coverage is seen as a limiting factor, even though Citebase indexes over 200,000 papers from arXiv. Non-physicists were frustrated at the lack of papers from other sciences. The principle of citation searching of open access archives has thus been demonstrated and need not be restricted to current users. Since the evaluation, Citebase has become a featured service of the ArXiv physics eprint archives.
"(Citebase) is a potentially critical component of the scholarly information architecture"
Paul Ginsparg, founder of arXiv

"I believe that ResearchIndex and Citebase are outstanding examples (of compellingly useful tools). These tools still have to be perfected to a point where their use is essential in any research activity. They will have to become clearly more pleasant, more informative and more effective than a visit to the library or the use of one's own knowledge of the literature. Much, much more! And I, for one, believe that they are coming quite near to this. But relatively few people realized this until now, even in these more technology prone fields of study."
Professor Imre Simon, September98-Forum, 24th November 2002

1 Introduction

Citation analysis and impact ranking are classical tools that are used not just by researchers but by policy makers who shape research. Developed by Garfield since the 1950s, citation indexing became the foundation for a series of products from ISI, most notably the "first multidisciplinary citation index to the scientific literature", the Science Citation Index (SCI). Merton (1979) described how citation indexing systematically identifies "links between the work of scientists that could be put to use both for searching the literature and for exploring cognitive and social relationships in science". With the development of Web of Science and more recently Web of Knowledge, ISI has migrated the SCI online, surely its natural medium with the facility for representing those "cognitive links" as simple hypertext links between citing and cited items.

It has been noted that while Garfield’s basic intentions were "essentially bibliographic", he has conceded that "no one could have anticipated all the uses that have emerged from the development of the SCI" (Guedon 2001). One of these uses is co-citation analysis (Small 1973), which makes possible the identification of emerging trends, or 'research fronts', which today can be visualised using powerful computational techniques (Chen and Carr 1999).

Another use, however, was to divert the SCI into a new business as a career management tool. As a result, Guedon claims that in "introducing elitist components into the scientific quest for excellence, SCI partially subverted the meaning of the science game".

New Web-based citation indexing services, such as ResearchIndex (also known as CiteSeer; Lawrence et al. 1999) and Citebase from the Open Citation (OpCit) Project, are founded on the same basic principles elaborated by Garfield (1994). Unlike Web of Knowledge which indexes core journal titles, these new services index full-text papers that can be accessed freely by users on the Web, and the indexing services are also currently free. While it is possible that open access indexing services founded on open access texts could re-democratise the role of citation indexing, there is no doubt these services will offer qualitatively different services from those provided by ISI: "Newer and richer measures of 'impact' ... will be not only accessible but assessable continuously online by anyone who is interested, any time" (Harnad 2001). According to Lawrence (2001), open access increases impact.

An exemplary case for open access to scholarly communications has been outlined by Suber (2003), who earlier  commented that the "greatest benefit" of open access content services that are free to users will be "to provide free online data to increasingly sophisticated software which will help scholars find what is relevant to their research, what is worthy, and what is new" Suber (2002). Citebase is an example of exactly that.

Despite the apparent advantage of open access, critical questions still have to be asked of these new services: are they useful and usable for the purposes of resource discovery and measuring impact? This report seeks to answer these questions based on an evaluation of Citebase, a citation-ranked search service. In the course of the investigation, some pointers to the resolution of these wider issues are also revealed.

2 Background to the evaluation

2.1 Open Citation Project

Since 1999, the Open Citation (OpCit) Project ( has been developing tools and services for reference linking and citation analysis of scholarly research papers in large open access eprint archives (Hitchcock et al. 2002). Most of the data collected and many of the services provided by OpCit have converged within a single interface, Citebase, a citation-ranked search and impact discovery service. The OpCit project completed its period of funding from the Joint NSF - JISC International Digital Libraries Research Programme at the end of 2002. As the project will be outlived by Citebase, it is appropriate to evaluate the project by means of the user response to this interface.

Other services developed by the project, such as an application programming interface for reference linking, have been evaluated separately (Bergmark and Lagoze 2001). software for creating open access Web-based archives (Gutteridge 2002), receives feedback from its already extensive list of registered implementers, which informs continuing development of new versions of the software.

2.2 About Citebase

Citebase, described by Hitchcock et al. (2002), indexes the citations from published research papers stored in the larger open access, disciplinary archives - currently arXiv (, CogPrints ( and BioMed Central ( Just prior to the evaluation Citebase had records for 230,000 papers, indexing 5.6 million references.

By discipline, approximately 200,000 of these papers are classified within arXiv physics archives. Thus, overwhelmingly, the current target user group for Citebase is physicists. The impact being made by the Open Archives Initiative (OAI; Van de Sompel and Lagoze 2002), which offers a technical framework for interoperability between digital archives, should help extend coverage significantly to other disciplines (Young 2002), through the emphasis of OAI on promoting institutional archives (Crow 2002). Hitchcock (2003) has monitored the growth of open access eprint archives, including OAI archives.

It is clear that a strong motivation for authors to deposit papers in institutional archives is the likelihood of subsequent inclusion in powerful resource discovery services which also have the ability to measure impact. For this reason there is a need to target this evaluation at prospective users, not just current users, so that Citebase can be designed for an expanding user base.

Citebase harvests OAI metadata records for papers, additionally extracting the references from each paper. The association between document records and references is the basis for a classical citation database. Citebase is sometimes referred to as “Google for the refereed literature”, because it ranks search results based on references to papers.

Citebase offers both a human user interface (, and an Open Archives (OAI)-based machine interface for further harvesting by other OAI services.

The primary Citebase Web user interface (Figure 2.1) shows how the user can classify the search query terms (typical of an advanced search interface) based on metadata in the harvested record (title, author, publication, date). In separate interfaces, users can search by archive identifier or by citation. What differentiates Citebase is that it also allows users to select the criterion for ranking results by Citebase processed data (citation impact, author impact) or based on terms in the records identified by the search, e.g. date (see drop-down list in Figure 2.1). It is also possible to rank results by the number of 'hits', a measure of the number of downloads and therefore a rough measure of the usage of a paper. This is an experimental feature to analyse both the quantitative and the temporal relationship between hit (i.e. usage) and citation data, as measures as well as predictors of impact. Hits are currently based on limited data from download frequencies at the UK arXiv mirror at Southampton only.

Figure 2.1. Citebase search interface showing user-selectable criteria for ranking results (with results appended for the search terms shown)

The results shown in Figure 2.1 are ranked by citation impact: Maldacena's paper, the most-cited paper on string theory in arXiv at the time (September 2002), has been cited by 1576 other papers in arXiv. (This is the method and result for Q2.3 in the evaluation exercise described below.)

The combination of data from an OAI record for a selected paper with the references from and citations to that paper is also the basis of the Citebase record for the paper. A record can be opened from a results list by clicking on the title of the paper or on 'Abstract' (see Figure 2.1). The record will contain bibliographic metadata and an abstract for the paper, from the OAI record. This is supplemented with four characteristic services from Citebase:

'Hits' are a new and contentious measure, especially when based on limited data. Recent studies offer support for the use of reader data by digital libraries to complement more established measures of citation frequency, which reflect author preferences (Darmoni et al. 2002). At the Los Alamos National Laboratory Research Library, Bollen and Luce (2002) defined a measure of the consultation frequency of documents and journals, and found that ranking journals using this method differs strongly from a ranking based on the traditional impact factor and, in addition, corresponded strongly to the general mission and research interests of their user community. The method of correlating citation data with online usage data has been used to investigate new bibliometric measures (Kurtz et al. 2003).

Another option presented to users from a results list is to open a PDF version of the paper (see Figure 2.1). This option is also available from the record page for the paper. This version of the paper is enhanced with linked references to other papers identified to be within arXiv, and is produced by OpCit. Since the project began, arXiv has been producing reference linked versions of papers. Although the methods used for linking are similar, they are not identical and OpCit versions may differ from versions of the paper available from arXiv. An important finding of the evaluation is whether reference linking of full-text papers should be continued outside arXiv. An earlier, smaller-scale evaluation, based on a previous OpCit interface (Hitchcock et al. 2000), found that arXiv papers are the most appropriate place for reference links because users overwhelmingly use arXiv for accessing full texts of papers, and references contained within papers are used to discover new works.

3 Description of the evaluation

The OpCit evaluation of Citebase took the form of a two-part Web-based questionnaire, designed to test Citebase in two ways: The test invited users to participate in a practical exercise and then to offer views on the service. Background information was also sought on how this new service might fit in with existing user practices. In this way the evaluation aimed to combine objectivity with subjectivity, overcoming some of the limitations of purely subjective tests.

The evaluation was performed over four months from June 2002, when the first observational tests took place, to the end of October 2002 when a closure notice was placed on the forms and the submit buttons were disabled.

The evaluation was managed by the OpCit project team in the IAM Group at Southampton University, the same team that reported on the evaluation of the forerunner eLib-funded Open Journal Project (Hitchcock et al. 1998). The arXiv Cornell partners in the project assisted with design and dissemination.

Observed tests of local users were followed by scheduled announcements to selected discussion lists for JISC and NSF DLI developers, OAI developers, open access advocates and international librarian groups. Finally, following consultation with our project partners at arXiv Cornell, arXiv users were directed to the evaluation by means of links placed in abstract pages for all but the latest papers deposited in arXiv.

3.1 Scope of the evaluation

The following elements of Citebase were a particular focus of the evaluation: Given the wide prospective user base, what was evaluated was not just the current implementation of Citebase, but the principle of citation-based navigation and ranking.

3.2 Purpose of the evaluation

The evaluation sought to:
  1. evaluate the usability of Citebase (can it be used simply and reliably for the purpose intended)
  2. assess the usefulness of Citebase (how does it compare and fit in with other services)
  3. measure user satisfaction with Citebase
  4. raise awareness of Citebase
  5. inform ongoing development of Citebase

3.3 Methods

The evaluation used two methods to collect data: The questionnaire was first tested by observation using local users at Southampton University. The wider community was made aware of the evaluation by means of staged announcements to selected discussion lists, and by links from the project and partner Web sites, notably from the abstract pages of all but the latest papers in arXiv, and from other Web pages serving physicists, PhysNet - "the worldwide Network of Physics Departments" (, and the CERN library (

After removing blanks, duplicates and test submissions, a total of 195 valid submissions of Form 1 were received. Of these users, 133 also completed Form 2, which was linked from the submit button of Form 1.

3.4 Discussion of the methods

Effective evaluation techniques include working intensively with a small group of people and applying the methodology of usability testing, where users are assigned a set of specific tasks to complete. The initial observed tests using the practical exercise in Form 1 satisfied these criteria and provided preliminary feedback.

As already indicated, Citebase is aimed at a much wider user group, both now and in the future, and the evaluation had to be extended to a representative section of those users. Open invitation is one way of achieving this. There are drawbacks to inviting evaluation based on a Web-only questionnaire, most obviously the lack of direct contact with users, and the consequent loss of motivation and information. Balancing this should be simplicity, easy accessibility and continuous availability. Web surveys have widened use and reduced the costs of survey techniques, but introduce new complexities (Gunn 2002). Efforts were made to ensure the forms were usable, based on the observed tests, and that Citebase offered a reliable service during the period of the evaluation. Availability of forms and service were monitored and maintained during the period of evaluation.

A perennial problem with forms-based evaluation, whether users are remote or not, is that badly designed forms can become the object of the evaluation. In tests of this type, where most users are experiencing a service for the first time, observation suggests that users may have understood the service more intuitively had they just looked at it as a search service rather than being introduced to it via step-by-step questions. Citebase was promoted only minimally prior to the investigation. This raises the question of whether the service to be evaluated, Citebase, should have been promoted more extensively. This would have increased familiarity, but it was felt this would make it more difficult to attract users to the evaluation unless those users were being brought to Citebase via the evaluation.

In contrast to Web forms, usage logs are an impeccable record of what people actually do, although there are problems of interpretation, and there are no standards for the assessment of Web logs.

The response to the evaluation from arXiv physicists, the primary target user group, was a little below expectations, although replies from other users were higher than expected. An earlier survey of users of eprint archives received nearly 400 replies from arXiv users (Hunt 2001). It is likely the lower number of respondents to the evaluation was due to the method of linking from arXiv to the evaluation. For the earlier survey, arXiv linked directly from a notice on its home page to the Web form. In this case abstract pages for papers in arXiv linked to the corresponding Citebase records. To get users to the evaluation form required that a linked notice be inserted temporarily in the Citebase records (Figure 3.1).

Figure 3.1 Adding a temporary notice to Citebase records to attract arXiv users to participate in this survey

As a means of bringing arXiv users to Citebase on an ongoing basis, this is an ideal, task-coupled arrangement. From the perspective of the evaluation, however, users were expected to follow two links to reach the evaluation, and were thus required to take two steps away from their original task. Since there was no direct link to the evaluation from the arXiv home page, and therefore no prior advocacy for, or expectation of, Citebase or the evaluation, perhaps it should not be surprising that the response did not match the earlier survey.

Usage of Citebase would have been affected for the same reason; also by a prominent notice:

Citebase (trial service, includes impact analysis)

placed alongside the new links to Citebase in arXiv (Figure 1 in Hitchcock et al. 2002).

Since the evaluation the Citebase developer (Tim Brody) has worked with our arXiv partners to refine Citebase. The trial notices have been removed and in February 2003 Citebase became a full featured service of arXiv.

4 Preparing Citebase for evaluation

Citebase is a large and dynamic database, the complexities of which must be hidden from the user while allowing the underlying power to be exploited.

One area of concern for Citebase were the descriptions, support and help pages, a vital part of any new and complex service. There was some reorganisation of this material, and new pages were added. This is an ongoing process and will continue to be informed by users.

Terminology was another aspect raised leading up to the evaluation. Terms used in the evaluation form such as "most cited" can be interpreted as the largest number of citations for an author or the largest average number of citations per paper for the same author. On the form this was revised (Q2.1). More generally, efforts were made to make terminology in Citebase comparable with ISI.

If bibliographic tools have been subverted, whether by design or not, to serve as career management tools, there is no hiding from the fact that new, experimental services will produce contentious results. This was a particularly acute concern during the preparation of Citebase for testing. A warning notice was added prominently to the main search page:

Citebase is currently only an experimental demonstration. Users are cautioned not to use it for academic evaluation yet. Citation coverage and analysis is incomplete and hit coverage and analysis is both incomplete and noisy.

Citebase was incomplete during the evaluation because new arXiv papers and their references were not harvested once the evaluation began in June. It was decided the data should be static during the evaluation, to ensure all users were evaluating the same object (some minor changes were made during the evaluation period, and these are highlighted in section 4.1). In arXiv, papers with numbers before 0206001 (June) had a link to Citebase, but not those deposited after.

Also, not all references could be extracted from all papers, which clearly would affect the results of citation impact. Techniques and software for automated reference extraction have been discussed by Bergmark (2000). Since the evaluation closed Citebase data have been brought up-to-date, and the reference parsing algorithm has been refined to improve extraction rates. An open source version of this software is available as ParaTools (

Warnings were also strengthened, after much discussion, around the 'hits' data graphs displayed in Citebase records (Figure 4.1). Reservations about this feature were expressed by arXiv Cornell colleagues, for the following reasons:

This feature needs to be examined carefully in the light of the results of the evaluation. However, the potential for usage measures in formal research assessment is undeniable (Harnad 2002). Citebase could serve to enrich the accuracy, equity and diversity of scientometric assessment of research productivity impact.

Figure 4.1. Citation/Hit History graph in a Citebase record, with prominent Caution! notice

4.1 Updating Citebase during the evaluation

In principle there should be no changes to the object being investigated during an evaluation. In practice, for a live, developing service such as Citebase there is always pressure to make changes and update it, especially over a four month evaluation period as in this case. Simply harvesting the daily submissions to arXiv materially changes Citebase, so this had to stop for the duration, with consequences that were noticed by some users. Some updates were essential, however. Table 4.1 highlights changes to Citebase that may have had some effect on the results of the evaluation.
Table 4.1. Citebase updates (moved to live version on 29th August), and possible effects on the evaluation
Citebase changes/updates Possible effect on evaluation (Form 1)
On Citebase search results page (Figure 2.1), add explicit 'Abstract/PDF' links to records (some users did not realise that clicking a title brings you to the abstract) Q2.3
New layout for internal links within Citebase record pages  Q2.4
'Linked PDF' label on Citebase record pages replaced by green 'PDF' graphic Q2.6a (full-text download)
Hits/citations graphs now on a different scale, hits warning added Q2.4-, Q3.1
* Other warnings added 13th September:
No update during study period
Incomplete coverage in ArXiv
Incomplete success of reference detection algorithm

5 Design of the evaluation forms

Users were presented with two evaluation forms to complete. Form 2 involved a simple measure of user satisfaction with the object being evaluated, Citebase, and was reached by responding to Form 1, which has four sections designed to: The following sections should be read with reference to Form 1 (

5.1 User context

Based on the broad coverage of Citebase and the scope of the planned announcements of the evaluation, it was anticipated that users would include not just physicists, but would extend to other users such as mathematicians, computer scientists and information scientists (Q1.1). Evaluators could specify other interests as necessary. Since the majority of evaluators, but not all, will also be users of arXiv, it was important to learn how this breaks down and to identify how this might quantitatively affect the results (Q1.2). It would also help to know how arXiv users currently discover new papers (Q1.3) as this will suggest possible routes into new discovery services such as Citebase.

Similarly, since Citebase will extend coverage to new OAI archives, it is helpful to know the level of awareness of OAI among evaluators (Q1.4) , and whether they use other OAI services (Q1.5).

As with all other sections on the evaluation forms, this section ends by inviting open comments from evaluators, which can be used to comment on any aspect of the evaluation up to this point.

5.2 Practical exercise

This is the critical phase of the evaluation, inviting evaluators to try key features of Citebase, identified in section 2, based on a set practical exercise. The subject chosen for the exercise, string theory, is of relevance to many physicists who use arXiv, but no prior knowledge of the subject was required to complete the exercise.

At this point users were prompted to open a new Web browser window to view the main Citebase search interface. It was suggested this link could have been placed earlier and more prominently, but this was resisted as it would have distracted from the first section.

Questions 2.1-2.3 involved performing the same task and simply selecting a different ranking criterion from the drop-down list in the search interface (Figure 2.1). Selectable ranking criteria is not a feature offered by popular Web search engines, even in advanced search pages, which the main Citebase search page otherwise resembles. The user's response to the first question is therefore important in determining the method to be used, and Q2.1 might be expected to score lowest, with familiarity increasing for Q2.2 and Q2.3. Where Q2.1 proved initially tricky, observed tests revealed that users would return to Q2.1 and correct their answer. We have no way of knowing to what extent this happened in unobserved submissions, but allowance should be made for this when interpreting the results.

The next critical point occurs in Q2.4, when users are effectively asked for the first time to look below the search input form to the results listing for the most-cited paper on string theory in arXiv (Q2.3). To find the most highly cited paper that cites this paper, notwithstanding the apparent tautology of the question, users must recognise they have to open the Citebase record for the most-cited paper by clicking on its title or on the Abstract link. Within this record the user then has to identify the section 'Top 5 Articles Citing this Article'. To find the paper most often co-cited with the current paper (Q2.5) the user has to scroll down the page, or use the link, to find the section 'Top 5 Articles Co-cited with this Article'.

Now it gets slightly harder. The evaluator is asked to download a copy of the full-text of the current paper (Q2.6a). What the task seeks to determine is the user's preference for selecting either the arXiv version of the paper or the OpCit linked PDF version. Both are available from the Citebase record. A typical linked PDF was illustrated by Hitchcock et al. (2000). Originally the Citebase record offered a 'linked PDF', but during the evaluation the developer changed this to a PDF graphic (Table 4.1). The significance of omitting 'linked' is that this was the feature differentiating the OpCit version. Given that it is known physicists tend to download papers in Postscript format rather than PDF (, it is likely that a simple PDF link would have little to recommend it against the link to the arXiv version.

As a check on which version users had downloaded, they were asked to find a reference (Q2.6b) contained within the full text (and which at the time of the evaluation was not available in the Citebase record, although it appeared in the record subsequently). To complete the task users had to give the title of the referenced paper, but this is not as simple as it might be because the style of physics papers is not to give titles of papers in references. To find the title, the user would need to access a record of the referenced paper. Had they downloaded the linked version or not? If so, the answer was one click away. If not, the task was more complicated. As final confirmation of which version users had chosen, and how they had responded subsequently, users were asked if they had resorted to search to find the title of the referenced paper. In fact, a search using Citebase or arXiv would not have yielded the title easily.

In this practical exercise users were asked to demonstrate completion of each task by identifying an item of information from the resulting page, variously the author, title or URL of a paper. Responses to these questions were automatically classified as true, false or no response. Users could cut-and-paste this information, but to ensure false responses were not triggered by mis-keying or entering an incomplete answer, a fuzzy text matching procedure was used in the forms processor.

Although this is an indirect measure of task completion, the results of this exercise can be read as an objective measure showing whether Citebase is a usable service. As an extra aid to judge the efficiency with which the tasks are performed, users were asked to time this section. One idea was to build a Javascript clock into the form, but this would have required additional user inputs and added to the complexity of the form.

5.3 Views on Citebase

By this stage users might be excited, exhausted or exasperated by Citebase (or by the evaluation), but they are now familiar with its features, and in this section are asked for their views on these.

Questions 3.1 and 3.2 enquire about Citebase as it is now and as it might be, respectively. It is reasonable to limit choices in the idealised scenario (Q3.2) so that users have to prioritise desired features. Users are likely to be more critical of the actual service, so it seems safe to allow a more open choice of preferred features.

Citebase has to be shaped to offer users a service they cannot get elsewhere, or a better service. Q3.3 seeks to assess the competition. This part of the evaluation is concluded by asking the user for a view on Citebase, not in isolation, but in comparison with familiar bibliographic services.

5.4 Follow-up and submission

As well as the necessary courtesies to users, such as offering follow-up in the form of a report and results, there was a practical motive for signing-up users for further evaluation. Citebase has certainly changed as a result of the evaluation, and this will create a motivated group of users willing to test the changes.

There is a second part to the evaluation, which is displayed to users automatically on submission of Form 1. It became apparent from observed tests that users do not always wait for a response to the submission and may miss Form 2, so a clear warning was added above the submission button on Form 1.

On submission the results were stored in a MySQL database and passed to an Excel spreadsheet for analysis.

5.5 Response and Form 2

The following section should be read with reference to Form 2 (,

Form 1 prompted users to respond to specific questions and features, and gives an impression of their reaction to the evaluated service, but does not really explore their personal feelings about it. A recommended way of tackling this is an approach based on the well-known Software Usability Measurement Inventory (SUMI) form of questionnaire for measuring software quality from the end user's point of view. Form 2 is a short implementation of this approach which seeks to discover:

Experience has shown that users rush through this form within a few minutes if it is seen immediately after the first form. It is thus a rough measure of satisfaction, but when structured in this way can point to areas of concern that might otherwise go undetected.

Four response options, ranging from very positive to very negative, are offered for each of four statements in each section. These responses are scored 2 to -2. A neutral response is not offered, but no response scores zero. A statement that users typically puzzle over is 'If the system stopped working it was not easy to restart it', before choosing not to respond if the system did not fail at any stage. Users often query this, but an evaluation, especially where users are remote from testers, has to anticipate all possible outcomes rather than make assumptions about reliability.

6 Observed testing

Volunteer users from the Physics Department and IAM Group at Southampton University worked in five separate pairs at various times at the end of June 2002, observed by one of the designers of the form (Steve Hitchcock, Arouna Woukeu). These tests were performed before open evaluation was announced to Web users. Form-based submissions from these users were recorded in the database, just as for later users, and are included in the summary quantitative results. Notes taken by the observer during the test were used to inform late revisions to the evaluation forms before wider announcements; in other respects the observed users performed the same exercise as all other users. It is not claimed that the observed evaluators are fully representative of the wider Citebase constituency, but the group is adequate to test the usability of the form (Nielsen 2000).

Scenario: Users worked with machines in their own environment. Users were assured it was not they who were being tested;  the system was being tested. Once they were in front of a machine with a working Web browser and connection, they were handed a printed copy of the evaluation forms as an aid and for notes, not instead of the online version. They were then given the URL to access evaluation Form 1, with no other instruction. Once started, observers were to avoid communication with users. Users were debriefed after completing the tasks.

Main findings (actions):

7 Usage: Citebase and the evaluation

7.1 Open announcements: effect on the evaluation

A by-product of the exercise was raising awareness of Citebase among target user and prospective user groups, especially among arXiv physicists to whom the service had not previously been announced. By monitoring Web usage logs for Citebase it is shown that usage increased from around 25-45 visitors per day before the evaluation began to 660 daily visitors at its peak during the evaluation. Further, staging announcements to lists enabled response levels to be tracked for different user groups.

Following actions taken to improve the experience for users, the evaluation was announced to selected open discussion lists in a phased programme during July 2002. Announcements were targetted at:

The effect of these announcements in terms of the number of responses to the evaluation and the level of usage of Citebase can be seen in Figures 7.1 and 7.2, respectively.

Figure 7.1. Chart of daily responses to evaluation Form 1(July-November 2002)

Figure 7.2. Citebase usage: summary statistics for July 2002 showing number of distinct visits (yellow chart) to (excludes all hits from and from (DP9), but includes search engines (effect visible in red chart))

It can be seen that the highest response to the evaluation during the period of open announcements occurred between 12-14 July following announcements to open access advocates (Figure 7.1), but Citebase usage in July was highest on the 22nd (Figure 7.2) after announcements to library lists.
Table 7.1: Citebase usage spikes (unique site visits) attributed to list announcements
Date (July) No. of visits Suspected source of users
22nd 207 Delayed reaction to library mails over a weekend
12th 175 OAI, Sept-Forum, FOS-Forum
15th 159 D-Lib Magazine
29th 138 PhysNet?
8th 109 Possibly delayed reaction to JISC, DLI mails over a weekend

7.2 ArXiv links to Citebase: bringing physicists to the evaluation

As has been noted already, physicists are likely to be the largest user group for Citebase given its extensive indexing of physics papers in arXiv. Links to Citebase records first appeared in arXiv abstracts on 20th August 2002. The effect on usage of Citebase was almost immediate, with peak usage occurring on 22nd August, as can be seen in Figure 7.3.

Figure 7.3. Citebase usage: summary statistics for August 2002 showing number of distinct visits (yellow chart) to (excludes all hits from and from (DP9), but includes search engines)

The impact of arXiv links on usage of Citebase was relatively much larger than that due to list announcements, as can be seen in Figure 7.4 in the column heights for July (list announcements) against August, September and October (arXiv links) (ignoring the red chart which emphasises the effect of Web crawlers rather than users).

Figure 7.4. Usage statistics for from Dec 2001 to November 2002 (excludes all hits from and from (DP9), but includes search engines)
*image saved on 15 November 2002

Table 7.2 puts the growth of Citebase usage (by visits) in perspective over this period: prior to the evaluation (February-June), due to list announcements (July), due to new arXiv links (August), and during the first full month of arXiv links (September).
Table 7.2. Growth of visits to Citebase, February-September 2002 (yellow columns in usage charts)
February-June July August September
Average daily visits 25-45 85 211 402
Highest daily visits 95 (8th May) 207 (22nd) 660 (22nd) 567 (4th)

The effect of the arXiv links on the evaluation were materially different from the mailed links, however, because the links were to Citebase, and only indirectly from there to the evaluation (see section 3.4). Table 7.3 shows how efficiently Citebase users were turned into evaluators on the best days for submission of evaluation Form 1. It shows how list announcements taking users directly to the evaluation returned the highest percentage of daily submissions from all Citebase users. Although overall usage of Citebase generated by arXiv links was much larger than for list announcements, this was not effectively translated into more submissions of the evaluation.
Table 7.3: Turning Citebase users into evaluators
Date No. of evaluation forms returned (Figure 7.1) Percentage of Citebase visitors that day
July 12th 16 9.1
July 13th 8 6.1
July 15th  7 4.4
July 22nd 7 3.4
July 8th 6 3.4
August 21st 6 1.3
August 23rd 6 1.1
August 27th 6 1.0
August 22nd 6 0.9 HTTP server daily usage ( shows c.15,000 hosts connecting each day, i.e. approximately 3.3% of arXiv visitors become Citebase users. The challenge for Citebase, highlighted by these figures, is to attract a higher proportion of arXiv users. Since September usage of Citebase has increased by 250%. What is not yet known is what proportion of arXiv usage is mechanical downloads, just keeping up with the literature, to be read later offline. Citebase will make little difference to this type of activity, but instead will help more active users, and here its proportionate share of users may already be much higher.

8 Results: Form 1 - using Citebase

Valid submissions to Form 1 ( were received from 195 evaluators.

8.1 About the evaluators

Q1.1 Subject interests of evaluators
Mathematicians 13 Computer scientists 15 Information scientists 33 Physicists 69 Other 60 Blank 5 Total 195
Other users included: Librarians (13), Cognitive scientists (10), Biologists (5), Cognitive neuroscientists (3), Health scientists (3), Medical psychiatrists (2), Sociologists (2), Publishers (2), and a teacher, information professional, behavioural geneticist, media specialist, philosopher, geomorphologist, engineer, economist, technical marketer, undergraduate.

The backgrounds of evaluators are broadly based, mostly in the sciences, but about 10% of users were non-scientists. This would appear to suggest greater expectation of OAI-based open access archives and services in the sciences, if this reflects a broad cross-section of the lists mailed (see section 7.1).

About a third of evaluators were physicists, although the number of physicists as a proportion of all users might have been expected to be higher given the concentration of Citebase on physics. (Physicists can be notoriously unfond of surveys, as the ArXiv administrators warned us in advance!)

Among non-scientists, as the highlighted comment below indicates, there may be a sense of exclusion. This is a misunderstanding of the nature of open access archives and services. No disciplines are excluded, but services such as Citebase can only act on major archives, which currently are mostly in the sciences. The primary exception is economics, which has distributed archives indexed by RePEc (

User comment
"As usual, I find myself an "outsider" in discussions of things that will be important to me very soon. I find there is no category for me to go into. You guys need to look beyond geekdom to think about ordinary social scientists, librarians, educationists."

It is true, if this is what is meant by the "outsider" above, that Q1.1 in this evaluation anticipated that evaluators would mostly be scientists of certain types, as shown in Figure 8.1. It must also be added that the Citebase services of impact-based scientometric analysis, measurement and navigation are intended in the first instance for research-users, rather than lay-users, because the primary audience for the peer-reviewed research literature is the research community itself.

Q1.2 Have you used the arXiv eprint archive before?

Daily Regularly Occasionally (less than monthly) No
56 (50) 26 (11) 28 (3) 79 (5)

Physicists in this sample tend to be daily users of arXiv. Non-physicists, noting that arXiv has smaller sections on mathematics and computer science, tend to be regular or occasional users of arXiv (Figure 8.1). Beyond these disciplines most are non-users of arXiv, and thus would be unlikely to use Citebase given its present coverage.

Figure 8.1. Correlation between subject disciplines and arXiv usage (x axis: Physics=4, Maths=3, Computer=2, infoScience=1, Other=0; y axis: 4=daily usage, 3=regular, 2=occasional, 1=don't use). Physicists are more likely to use arXiv daily, non-physicists are less likely to use arXiv: correlation= 0.754522, N=189, p<0.001

Q1.3 If you have used arXiv, which way do you access arXiv papers? (you may select one or more)

Most arXiv users in this study access new material by browsing, rather than by alerts from arXiv. The relatively low ranking of the latter was unexpected. There is some encouragement for services such as Citebase (note, at this stage of the evaluation users have not yet been introduced to Citebase) in the willingness to use Web search and reference links to access arXiv papers (second and third most popular categories of access). It is possible, as mentioned above, that the Citebase evaluators were a biased sample of arXiv daily users who do not download mechanically.

Figure 8.2. Accessing arXiv papers

Q1.4 Had you heard of the Open Archives Initiative?

Yes No
99 (11) 86 (55)
( ) physicists only

OAI is familiar to over half the evaluators, but not to many physicists (Figure 8.3a). The latter is not surprising. OAI was originally motivated by the desire to encourage researchers in other disciplines to build open access archives such as those already available to physicists through arXiv, although the structure of Open Archives, unlike arXiv, is de-centralised (Lynch 2001).



Figure 8.3 Correlations with prior knowledge of OAI: a, with subject discipline (x axis: physics=4, maths=3, computer=2, infoScience=1, other=0), physicists are least likely, information scientists most likely to have heard of OAI, correlation= -0.46758, N=189, p<0.001; b, with level of arXiv usage (x axis: daily usage=4, regular usage=3, occasional usage=2, no usage=1), those who use arXiv least or not at all are more likely to have heard of OAI, correlation=-0.35072, N=189, p=<0.001 (y axis: 2=heard of OAI, yes, 1=have not heard of OAI)

Q1.5 Have you used any other OAI services? (you may select one or more)

arc 8 myOAI 10 kepler 6 Other 2 No response 178

Although OAI has made an impact among most non-physicist evaluators - again probably preordained through list selection - there is clearly a problem attracting these users to OAI services. Either current OAI services are not being promoted effectively, or they are not providing services users want -- or this may be merely a reflection of the much lower availability of non-physics OAI content to date! As an OAI service, this result shows the importance for Citebase of learning the needs of its users from this evaluation, and of continuing to monitor the views of users. More generally, this result suggests there are stark issues for OAI and its service providers to tackle. To be fair, the services highlighted on the questionnaire are mainly research projects. It is time for OAI services to address users.

8.2 Practical exercise: building a short bibliography

Q2.1 Who is the most-cited (on average) author on string theory in arXiv?
Correct 141 (45) Incorrect 20 (8) No answer 34 (15)
Q2.2 Which paper on string theory is currently being browsed most often in arXiv?
Correct 133 (41) Incorrect 16 (8) No answer 46 (19)
Q2.3 Which is the most-cited paper on string theory in arXiv?
Correct 145 (48) Incorrect 9 (2) No answer 41 (18)
Q2.4 Which is the most highly cited paper that cites the most-cited paper above? (critical point)
Correct 122 (44) Incorrect 26 (5) No answer 47 (19)
Q2.5 Which paper is most often co-cited with the most-cited paper above?
Correct 133 (46) Incorrect 12 (3) No answer 50 (19)
Q2.6a  Download the full-text of the most-cited paper on string theory. What is the URL?
Correct 124 (42) Incorrect 13 (3) No answer 58 (23)
(Correct=Opcit linked copy 71 (15) +arXiv copy 53 (27))
Q2.6b In the downloaded paper, what is the title of the referenced paper co-authored with Strominger and Witten (ref [57])?
Correct 105 (35) Incorrect 27 (9) No answer 63 (24)
Q2.6c Did you use search to find the answer to 2.6b?
No 118 (40); Yes 18 (3)
( ) physicists only

Results from this exercise show that most users were able to build a short bibliography successfully using Citebase (Figure 8.4). The exercise introduced users to most of the principal features of Citebase, so there is a good chance that users would be able to use Citebase for other investigations, especially those related to physics. The yellow line in Figure 8.4a, indicating correct answers to the questions posed, shows a downward trend through the exercise, which is most marked for Q2.6 involving downloading of PDF full texts. Figure 8.4b, which includes results for physicists only, shows an almost identical trend, indicating there is not a greater propensity among physicists to be able to use the system compared with other users..

As anticipated, Q2.4 proved to be a critical point, showing a drop in correct answers from Q2.3. The upturn for Q2.5 suggests that user confidence returns quickly when familiarity is established for a particular type of task. Similarly, the highest number of correct answers for Q2 .3 shows that usability improves quickly with familiarity of the features of a particular page. At no point in Figure 8.4 is there evidence of a collapse of confidence or of unwillingness among users to complete the exercise.

The incidental issue of which PDF version users prefer to download, OpCit or arXiv version (Q2.6a), was not conclusively answered, and could not be due to the change in format on the Citebase records for papers (Table 4.1). It can be noted that among all users, physicists displayed a greater preference to download the arXiv version.


Figure 8.4. Progress in building a short bibliography through Q2.1-2.6b in evaluation Form 1 (T=true, correct answer, F=false, N=no response): a, All users; b, Physicists only

Physicists generally completed the exercise faster than other users (Figure 8.5a). Almost 90% of users (100% of physicists) completed the exercise within 20 mins, with approximately 50% (55% physicists) finishing within 10 mins. There appears to be some correlation between subject disciplines and level of arXiv usage with the time taken to complete the exercise (Figure 8.5), although neither correlation is statistically significant. Taken together these results show that tasks can be accomplished efficiently with Citebase regardless of the background of the user.

Time taken to complete section 2, ( ) physicists only

1-5 minutes 5-10 10-15 15-20 20-25 25-30 30+ ? Total
13 (6) 60 (21) 36 (14) 17 (5) 9 (0) 6 (0) 2 (0) 5 (2) 147


Figure 8.5 Correlations between time taken to complete section 2 and: a, subject disciplines (x axis: physics=4, maths=3, computer=2, infoScience=1, other=0) correlation= -0.15, N=140, p<0.077, b, level of arXiv usage (x axis: daily usage=4, regular usage=3, occasional usage=2, no usage=1) correlation=-0.18, N=140, p<0.033

On the basis of these results there can be confidence in the usability of most of the features of Citebase, but the user comments in this section draw attention to some serious usability issues - help and support documentation, terminology - that must not be overshadowed by the results.

8.3 User views of Citebase

Q3.1 In your view, which are the most useful features of Citebase? (you may select one or more)

Links to citing and co-citing papers are features of Citebase that are valued by users (Figure 8.6), even though these features are not unique to Citebase. The decision to rank papers according to criteria such as these, and to make these ranking criteria selectable from the main Citebase search interface, is another feature that has had a positive impact with users. Citations/hit graphs appear to have been a less successful feature. There is little information in the data or comments to indicate why this might be, but it could be due to the shortcomings discussed in section 4 and it may be a feature worth persevering with until more complete data can be tested.

Figure 8.6. Most useful features of Citebase

Q3.2 What would most improve Citebase?

Users found it harder to say what would improve Citebase, judging from the number of 'no responses' (Figure 8.7). Wider coverage, especially in terms of more papers, is desired by all users, including physicists.

Figure 8.7. Improving Citebase

The majority of the comments are criticisms of coverage. Signs of the need for better support documentation reemerge in this section. Among features not offered on the questionnaire but suggested by users, the need for greater search precision stands out (Table 8.1).

Table 8.1. Other suggestions for improving Citebase
  • A way to get BIBTEX format
  • Ability to extract reference lists from paper
  • Author search clarity
  • Displayed comments from experts
  • Explanations in a more obvious place
  • Facilities to download references
  • Help files giving examples of common procedures
  • Include journal articles/references
  • Include journal references
  • Method for keeping track of search/browse path
  • More precision in indexing and therefore search
  • More refined search capabilities
  • Most-browsed graphic indicator
  • Remove ranking, etc.

Q3.3 What services would you use to compile a bibliography in your own work and field? (you may select one or more)

There is a roughly equal likelihood that users who participated in this survey will use Web-based services (e.g. Web search), online library services and personal bibliography software to create bibliographies (Figure 8.8). This presents opportunities for Citebase to become established as a Web-based service that could be integrated with other services. The lack of a dominant bibliography service, including services from ISI, among this group of users emphasises the opportunity (Table 8.2).

Figure 8.8. Creating personal bibliographies

Table 8.2. Bibliography services used most by evaluators
  • ISI Web of Science 16
  • PubMed 10 
  • SLAC Spires 8
  • Mathscinet 7
  • Google 6
  • ISI 7 (SCI 5; Scisearch, Social SciSearch 1)
  • arXiv 4
  • CiteSeer/ResearchIndex 4
  • Inspec 4
  • ADS 3
  • Medline 3
  • PsycInfo 3

Q3.4 How does Citebase compare with these bibliography services (assuming that Citebase covered other subjects to the degree it now covers physics)?

Citebase is beginning to exploit that opportunity presented by the lack of a dominant bibliography service (Figure 8.9), but needs to do more to convince users, even physicists, that it can become their primary bibliographic service.

Figure 8.9. Comparing Citebase with other bibliography services

Attempts to correlate how Citebase compares with other bibliographic services with other factors considered throughout the evaluation - with subject discipline, with level of arXiv usage, and time taken to complete section 2 - showed no correlations in any case (Figures 8.10-8.12). This means that reactions to Citebase are not polarised towards any particular user group or as a result of the immediate experience of using Citebase for the pre-set exercise, and suggests that the principle of citation searching of open access archives has been demonstrated and need not be restricted to current users.

Figure 8.10. Correlation between subject disciplines and views on how Citebase compares with other bibliography services (x axis: physics=4, maths=3, computer=2, infoScience=1, other=0; y axis: citebase compares "very favourably"=2, "favourably"=1, no response=0, "unfavourably"=-1), correlation= -0.00603, N=190, p<0.924. There is no meaningful correlation

Figure 8.11. Correlation between level of arXiv usage and views on how Citebase compares with other bibliography services (x axis: daily usage=4, regular usage=3, occasional usage=2, no usage=1; y axis: citebase compares "very favourably"=2, "favourably"=1, no response=0, "unfavourably"=-1), correlation= 0.014765, N=190, p<0.840. There is no meaningful correlation

Figure 8.12. Correlation between views on how Citebase compares with other bibliography services and time taken to complete section 2 (xaxis: citebase compares "very favourably"=2, "favourably"=1, no response=0, "unfavourably"=-1), correlation= 0.029372, N=144, p<0.727. There is no meaningful correlation

There is little opportunity in this section for users for users to compare, contrast and discuss features of Citebase that differentiate it from other services. In particular, Citebase offers access to full texts in open access eprint archives. It is an aspect that needs to be emphasised as coverage and usage widen. Comments reveal that some users appreciate this, although calls for Citebase to expand coverage in areas not well covered now suggest this is not always understood. It is not possible for Citebase to simply expand coverage unless there is recognition and prior action by researchers, as authors, of the need to contribute to open access archives. One interpretation is that users in such areas do not see the distinction between open access archives and services and paid-for journals and services, because they do not directly pay for those services themselves - these services appear to be free.

9 Results: Form 2 - user satisfaction with Citebase

Form 1 focussed on specifics: about the user; a series of tasks; about Citebase. Form 2 allowed users to express a more personal reaction to the service they had experienced. Form 2 was based on the Software Usability Measurement Inventory (SUMI) form of questionnaire for measuring software quality from the end user's point of view. Users were invited to indicate, from a predefined list, their degree of reaction, for or against, to a series of propositions about general features of the system tested. These propositions assessed the users' impression and command of the system, and the effectiveness and navigability of the system.

Form 2 could have been longer and explored other areas, but this may have inhibited the number of responses. As Form 2 was separate from Form 1 it was not expected that all users would progress this far. Of 195 users who submitted the first form, 133 completed Form 2 (

The summary results by question and section are shown in Table 9.1 and Figure 9.1.
Table 9.1. Satisfaction scores (Form 2)
Question 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Average score by Q. 0.92 0.79 1.39 1.05 0.41 1.17 0.83 1.02 0.65 1.07 1.42 0.99 0.92 0.27 0.57 0.26
Section Impression Command Effectiveness Navigability
Average by section 1.04 0.86 1.03 0.51

a   b
Figure 9.1. Average user satisfaction scores: a, by question, b, by section

The highest score was recorded for Q11, indicating that on average users were able to find the information required most of the time. Scoring almost as high, Q3 shows users found the system frustrating to use only some of the time.

The questions ranked lowest by score, Q14 and Q16, suggest that users agree weakly with the proposition that there were plenty of ways to find the information needed, and disagreed weakly with the proposition that it is easy to become disoriented when using the system.

Scores by section indicate that, overall, users formed a good impression of Citebase. They found it mostly to be effective for task completion (confirming the finding of Form 1, section 2), and they were able to control the system most of the time. The lower score for navigability suggests this is an area that requires further consideration.

It should be recalled that responses were scored between 2 and -2, depending on the strength of the user's reaction. In this context it can be seen that on average no questions or sections scored negatively; six questions scored in the top quartile, and two sections just crept into the top quartile.

Among users, scores were more diverse, with the total user score varying from 31 (maximum score possible is 32) to -25. Other high scores included 29, 28 and 27 (by five users). Only eight users scored Citebase negatively.

Submission of Form 2 completed the evaluation for the user.

10 Conclusions

Professor Imre Simon, quoted at the top of this report, perfectly sums up the results of the evaluation and the feelings of users towards Citebase: there is much scope for improvement but, as exemplified by Citebase, Web-based citation indexing of open access archives is closer to a state of readiness for serious use than had previously been realised.

The exercise to evaluate Citebase had a clear scope and objectives. Within the scope of its primary components, the search interface and services available from a Citebase record, it was found Citebase can be used simply and reliably for resource discovery. It was shown tasks can be accomplished efficiently with Citebase regardless of the background of the user.

The principle of citation searching of open access archives has been demonstrated and need not be restricted to current users.

More data need to be collected and the process refined before it is as reliable for measuring impact.As part of this process users should be encouraged to use Citebase to compare the evaluative rankings it yields with other forms of ranking.

Citebase is a useful service that compares favourably with other bibliographic services, although it needs to do more to integrate with some of these services if it is to become the primary choice for users.

The linked PDFs are unlikely to be as useful to users as the main features of Citebase. Among physicists, linked PDFs will be little used, but the approach might find wider use in other disciplines where PDF is used more commonly.

Although the majority of users were able to complete a task involving all the major features of Citebase, user satisfaction appeared to be markedly lower when users were invited to assess navigability than for other features of Citebase.

Perhaps one of the most important findings of the evaluation is that Citebase needs to be strengthened in terms of the help and support documentation it offers to users.

Coverage is seen as a limiting factor. Although Citebase indexes over 200,000 papers from arXiv, non-physicists were frustrated at the lack of papers from other sciences. This is a misunderstanding of the nature of open access services, which depend on prior self-archiving by authors. In other words, rather than Citebase it is users, many of whom will also be authors, who have it within their power to increase the scope of Citebase by making their papers available freely from OAI-compliant open access archives. Citebase will index more papers and more subjects as more archives are launched.

The wider objectives and aspirations for developing Citebase are to help increase the open-access literature. Where there are gaps in the literature - and there are very large gaps in the open-access literature currently - Citebase will motivate authors to accelerate the rate at which these gaps are filled. Research funders can provide stronger motivation for authors to self-archive by mandating that assessable work is to be openly accessible online (Harnad et al. 2003).


The Open Citation Project was funded between 1999 and 2002 by the Joint NSF - JISC International Digital Libraries Research Programme.

We are grateful to Paul Ginsparg, Simeon Warner and Paul Houle at arXiv Cornell for their comments and feedback on the design of the evaluation and their cooperation in helping to direct arXiv users to Citebase during the evaluation. Eberhard Hilf and Thomas Severiens at PhysNet and Jens Vigen at CERN were also a great help in alerting users to the evaluation.

Our local evaluators at Southampton University gave us confidence the evaluation was ready to be tackled externally. We want to thank Iain Peddie, Shams Bin Tariq, David Crooks, Jonathan Parry (Physics Dept.) and Muan H. Ng, Chris Bailey, Jing Zhou, Norliza Mohamad Zaini, Hock K.V. Tan and Simon Kampa.(IAM Dept.).

Finally, we thank all our Web evaluators, who must remain anonymous, but this in no way diminishes their vital contribution.


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