OA Impact Advantage

Laakso & Björk (2013) compare the citation impact of immediate Gold OA with delayed Gold and toll-access. They find that delayed-Gold journals average twice as many citations per article as toll-access journals and three times as many as immediate-Gold journals.

This is based on comparisons between different journals. But journals differ in both subject matter and quality -- and one of the ways to try to equate them to make them comparable for quality is to equate them for impact.

So if journals are not equated for subject matter and quality, one is comparing apples and oranges. But if immediate Gold OA, delayed-Gold and toll-access journals are equated for impact, one can't compare impact for delayed vs. immediate Gold -- in fact one can't compare the journals for citation impact at al!!

A feasible way to compare immediate-OA with delayed-access and toll-access is via Green OA based on within-journal comparisons instead of between-journal comparisons, by comparing articles published within the same journal and year that are and are not made Green OA. To do this one needs both the date of publication and the date the article was made Green OA.

It is impossible to get the OA date for webwide deposits in general, but for repository deposits it is possible.

We do have some very preliminary and partial data from the University of Minho repository, but the sample is still too small to do within-journal comparisons. Immediate Green OA articles do have more citations on average than Delayed Access articles (see Figures 2c and 3c) despite the availability of the automated "Almost-OA" Button during the delay period, but these citation counts are just absolute ones, rather than relative to within-journal matched toll-access controls. Hence these are likewise still comparisons between apples and oranges. (Note also that the large number of undeposited articles is likewise unmatched, and not based on their respective within-journal matched toll-access controls.)

The sample will grow as the number of Green OA mandates and repository deposits worldwide grows. The vast unused potential for immediate Green-OA and Almost-OA has long been known and noted -- most recently by Laakso (2014).

Gargouri, Yassine, Larivière, Vincent & Harnad, Stevan (2013) Ten-year Analysis of University of Minho Green OA Self-Archiving Mandate (in E Rodrigues, Ed. title to come)

Laakso, M., & Björk, B. C. (2013). Delayed open access: An overlooked high-impact category of openly available scientific literature. Journal of the American Society for Information Science and Technology.

Laakso, M (2014) Green open access policies of scholarly journal publishers: a study of what, when, and where self-archiving is allowed. Scientometrics (in press)

Open Access ≠ Open Access Journals. In AAAS's ScienceInsider, Jocelyn Kaiser reports the results of yet another survey showing that researchers want Open Access but do not provide it.

But if you ask the wrong questions, you get the wrong answers.

Open Access (OA) means free online access to peer-reviewed journal articles.

OA provides for researchers the advantage of maximizing the access, uptake, usage, applications, progress and impact of their research findings by making them accessible to all potential users, not just subscribers. Most researchers already know this.

There are two ways for researchers to provide OA:

--- (1) either researchers publish in an OA journal, which makes its article free for all online ("Gold OA");

--- (2) or researchers publish in their journal of choice but also self-archive their final peer-reviewed draft in their institutional OA repository, which makes it free for all online ("Green OA").

Gold OA has all the disadvantages mentioned and not mentioned by Kaiser: (i) not the author's established journal of choice; (iii) may have low or no peer-review standards (iii) may cost the author money to publish, out of scarce research funds.

That explains why most authors want OA but few provide Gold OA (as this latest Science survey yet again found).

About twice as many authors provide Green OA as Gold OA, but that's still very few: So what are the reasons authors don't provide Green OA?

Authors don't provide Green OA because they (i) fear it might be illegal; (ii) fear it might jeopardize publishing in their journal of choice; (iii) fear it might jeopardize peer-reviewed publishing itself.

The difference between the reasons why authors don't provide Gold OA and the reasons they don't provide Green OA is that the former are valid reasons and the latter are not.

But the solution is already being implemented worldwide, although Kaiser does not mention it:

Research funders and research institutions worldwide are mandating (requiring) Green OA.

Over 60% of journals already formally endorse immediate, unembargoed Green OA.

For the remaining 40% of articles, published in journals that embargo Green OA for 6, 12, 24 months or longer, they can be deposited as Closed Access (CA) instead of OA duriing the embargo: institutional repositories have a request-a-copy Button that allows users to request and authors to provide an email copy of any CA deposit with one click each ("Almost-OA").

So Green OA mandates can provide at least 60% immediate OA plus 40% Almost-OA. (This unused potential for immediate Green-OA and Almost-OA has long been known and noted -- most recently by Laakso (2014)).

And if Green OA mandates eventually make subscriptions unsustainable -- because Green OA from OA institutional repositories makes it possible for institutions to cancel their subscriptions -- then journals will cut costs (leaving all access-provision and archiving to the Green OA repositories), downsize and convert to Gold OA, providing peer review at a fair, affordable, sustainable price, paid for out of the institutions' subscription cancellation savings (not authors' research funds).

So mandatory Green OA is (i) legal, (ii) does not jeopardize authors' publishing in their journal of choice and (iii) does not jeopardize publishing or peer review:

Mandating Green OA merely provides Green OA (and Almost-OA) until journals convert to affordable Gold OA so that (i) authors can continue to publish in their established journal of choice; (ii) need not risk low or no peer-review standards (iii) need not pay to publish out of scarce research funds.

It would have been more complicated for the Science survey to explain the Green/Gold contingencies before asking the questions, but it would have been more informative than asking, as this survey did, "What is the Sound of One Hand Clapping?"

The outcome would have been that the vast majority of researchers will willingly comply with a Green OA mandate, exactly as had already been found by Swan & Brown's classic international JISC survey in 2005:

The Open Access (OA) citation advantage has been repeatedly demonstrated for Green OA, that is, articles published in any journal at all, but made open access by their authors by self-archiving them free for all online.

But the significant citation advantage for OA articles over non-OA articles -- which has been found in every field tested -- is based on comparing like with like: journal articles appearing in the same journal and year, and even sometimes matched for topic via title words.

Testing for a citation advantage of OA journals (Gold OA) over non-OA journals ("EC study finds low citation gains for gold open access") requires comparisons between journals, instead of between articles within the same journal. As a consequence, even if efforts are made to compare journals within the same field, there is no way to ensure that the journals cover the same subject matter, nor, perhaps even more important, to ensure that they are of the same quality. For journals do differ not only in subject matter but in the quality of their content.

As Eric Archambault notes, Gold OA journals are handicapped by the fact that they tend to be younger, and hence have not had a chance to establish a track record for either subject matter or quality.

But even for journals of the same age, and even if they are closely matched for subject matter, it is impossible to match them for quality. And to make it even worse, journal average citation counts ("journal impact factors") are sometimes taken as a proxy for quality! Hence equating journals for quality that way would guarantee that there could be no citation advantage between matched OA and non-OA journals!

The good news is that there is no reason to believe that the OA citation advantage that has been repeatedly demonstrated by within-journal comparisons using Green OA should not also generalize to OA provided by Gold OA -- for articles of comparable quality.

One last point: Our studies have found that the size of the OA advantage is itself correlated with quality (or at least with quality as measured by citation counts): The size of the Green OA advantage is greater in journals with higher average citation counts. We tentatively conclude that the citation advantage is greater for "more citable" articles. A lower quality article will not gain as much as a higher quality article from being made more accessible. OA may even lower the citation counts of low quality articles by levelling the playing field, making all articles accessible, and hence making it possible for authors to access, use and cite the best and most relevant articles, rather than being limited to the articles that their institutions can afford to access via institutional journal subscriptions or licenses.

Gargouri, Y., Hajjem, C., Lariviere, V., Gingras, Y., Brody, T., Carr, L. and Harnad, S. (2010) Self-Selected or Mandated, Open Access Increases Citation Impact for Higher Quality Research. PLOS ONE 5 (10) e13636

Gaulé, Patrick & Maystre, Nicolas (2011) Getting cited: Does open access help? Research Policy (in press)

G & M: "Cross-sectional studies typically find positive correlations between free availability of scientific articles (‘open access’) and citations… Using instrumental variables, we find no evidence for a causal effect of open access on citations. We provide theory and evidence suggesting that authors of higher quality papers are more likely to choose open access in hybrid journals which offer an open access option. Self-selection mechanisms may thus explain the discrepancy between the positive correlation found in Eysenbach (2006) and other cross-sectional studies and the absence of such correlation in the field experiment of Davis et al. (2008)… Our results may not apply to other forms of open access beyond journals that offer an open access option. Authors increasingly self-archive either on their website or through institutional repositories. Studying the effect of that type of open access is a potentially important topic for future research..."

What the Gaulé & Maystre (G&M) (2011) article shows -- convincingly, in my opinion -- is that in the case of paid hybrid gold OA, most of the observed citation increase is better explained by the fact that the authors of articles that are more likely to be cited are also more likely to pay for hybrid gold OA. (The effect is even stronger when one takes into account the phase in the annual funding cycle when there is more money available to spend.)

But whether or not to pay money for the OA is definitely not a consideration in the case of Green OA (self-archiving), which costs the author nothing. (The exceedingly low infrastructure costs of hosting Green OA repositories per article are borne by the institution, not the author: like the incomparably higher journal subscription costs, likewise borne by the institution, they are invisible to the author.) 

I rather doubt that G & M's economic model translates into the economics of doing a few extra author keystrokes -- on top of the vast number of keystrokes already invested in keying in the article itself and in submitting and revising it for publication. 

It is likely, however -- and we have been noting this from the very outset -- that one of the multiple factors contributing to the OA citation advantage (alongside the article quality factor, the article accessibility factor, the early accessibility factor, the competitive [OA vs non-OA] factor and the download factor) is indeed an author self-selection factor that contributes to the OA citation advantage.

What G & M have shown, convincingly, is that in the special case of having to pay for OA in a hybrid Gold Journal (PNAS: a high-quality journal that makes all articles OA on its website 6 months after publication), the article quality and author self-selection factors alone (plus the availability of funds in the annual funding cycle) account for virtually all the significant variance in the OA citation advantage: Paying extra to provide hybrid Gold OA during those first 6 months does not buy authors significantly more citations.

G & M correctly acknowledge, however, that neither their data nor their economic model apply to Green OA self-archiving, which costs the author nothing and can be provided for any article, in any journal (most of which are not made OA on the publisher's website 6 months after publication, as in the case of PNAS). Yet it is on Green OA self-archiving that most of the studies of the OA citation advantage (and the ones with the largest and most cross-disciplinary samples) are based.

I also think that  because both citation counts and the OA citation advantage are correlated with article quality there is a potential artifact in using estimates of article or author quality as indicators of author self-selection effects: Higher quality articles are cited more, and the size of their OA advantage is also greater. Hence what would need to be done in a test of the self-selection advantage for Green OA would be to estimate article/author quality [but not from their citation counts, of course!] for a large sample and then -- comparing like with like -- to show that among articles/authors estimated to be at the same quality level, there is no significant difference in citation counts between individual articles (published in the same journal and year) that are and are not self-archived by their authors.

No one has done such a study yet  -- though we have weakly approximated it (Gargouri et al 2010) using journal impact-factor quartiles. In our approximation, there remains a significant OA advantage even when comparing OA (self-archived) and non-OA articles (same journal/year) within the same quality-quartile. There is still room for a self-selection effect between and within journals within a quartile, however (a journal's impact factor is an average across its individual articles; PNAS, for example, is in the top quartile, but its individual articles still vary in their citation counts). So a more rigorous study would have to tighten up the quality equation much more closely). But my bet is that a significant OA advantage will be observed even when comparing like with like.

Stevan Harnad
EnablingOpenScholarship

Miguel, Sandra, Zaida Chinchilla-Rodriguez & Félix de Moya-Anegón (2011) Open Access and Scopus: A New Approach to Scientific Visibility From the Standpoint of Access. Journal of the American Society for Information Science and Technology (JASIST)http://dx.doi.org/10.1002/asi.21532

ABSTRACT: The last few years have seen the emergence of several open access (OA) options in scholarly communication, which can be grouped broadly into two areas referred to as gold and green roads. Several recent studies have shown how large the extent of OA is, but there have been few studies showing the impact of OA in the visibility of journals covering all scientific fields and geographical regions.This research presents a series of informative analyses providing a broad overview of the degree of proliferation of OA journals in a data sample of about 17,000 active journals indexed in Scopus. This study shows a new approach to scientific visibility from a systematic combination of four databases: Scopus, the Directory of Open Access Journals, Rights Metadata for Open Archiving (RoMEO)/Securing a Hybrid Environment for Research Preservation and Access (SHERPA), and SciMago Journal Rank] and provides an overall, global view of journals according to their formal OA status. The results primarily relate to the number of journals, not to the number of documents published in these journals, and show that in all the disciplinary groups, the presence of green road journals widely surpasses the percentage of gold road publications. The peripheral and emerging regions have greater proportions of gold road journals. These journals belong for the most part to the last quartile. The benefits of OA on visibility of the journals are to be found on the green route, but paradoxically, this advantage is not lent by the OA, per se, but rather by the quality of the articles/journals themselves regardless of their mode of access.

Miguel et al's (2011) article is very timely and useful in its SCOPUS-based quantification of the proportion of journals that are Green, Gold and Gray journals, across fields and countries.

It is also very useful in reviewing and supporting the advantages and primacy of Green OA.

But one of Miguel et al’s conclusions is incorrect:

"The benefits of OA on visibility of the journals are to be found on the green route, but paradoxically, this advantage is not lent by the OA, per se, but rather by the quality of the articles/journals themselves regardless of their mode of access."

The authors show, correctly, that, on average, Green journals (i.e., journals that formally endorse their authors' right to self-archive their articles) have higher impact factors than Gold and non-Green journals, across all fields.

These data are welcome, but they merely confirm what has been known for years now: Most of the top journals are already Green. (Over 60% of journals have been Green for many years now, as SHERPA Romeo has been showing -- and those include most of the top journals in just about every field. The top journals often also tend to have higher impact factors.)

But (alas!) it does not follow from the fact that Green journals have higher impact factors that their authors are actually providing Green OA! Far from it.

Between 5 and 25% of articles are being made Green OA (depending on field) today, and it is only Green OA mandates that significantly increase those percentages.

(Apart from the effect of mandates, the Green OA percentages themselves have been increasing glacially slowly across the years. And Green OA mandates apply to all articles, not just to articles in Green OA journals.)

The reason it became evident to universities and funders that Green OA mandates were necessary was precisely because Green publishers endorsements of their authors’ right to provide Green OA was not enough to induce most authors to provide Green OA.

Miguel et al’s article is helpful in that it supports Green OA (hence, indirectly, it also supports Green OA mandates), but it has unfortunately misinterpreted both the causality and the methodology underlying the studies demonstrating the Green OA citation advantage:

Miguel et al interpret the higher average impact factor of Green journals as the cause underlying the widely reported OA citation impact advantage, suggesting that it is not OA that causes the higher impact, but just the fact that more high-impact journals endorse Green OA.

But most of the studies demonstrating the OA impact advantage are based on comparing on comparing articles within the very same journal (Green OA articles vs. non-OA articles; Gold OA journals are of course omitted in these within-journal comparisons, because all of their articles are OA, so one cannot do compare the impact of OA and non-OA articles).

Hence all the reports of the Green OA impact advantage are based on within-journal effects, not between-journal effects.

Hence it is not relevant for the many reports of the Green OA advantage whether the journals are Green or Gray (Gold journals being eliminated in any case, for methodological reasons). It is also irrelevant what proportions of all journals are Green, Gold or Gray.

I think Miguel et al misinterpretation arises from two sources (not unique to Miguel et al):

(1) A general tendency to conceive of OA as a journal effect rather than an article effect (because of a narrow focus on journals, especially Gold OA journals, as the model for OA).

(2) A systematic ambiguity about the meaning of "Green," depending on whether one is thinking at the journal level or the article level:

(2a) At the journal level, "Green" (unlike "Gold") just means that the journal endorses author-provided Green OA -- it does not mean that the journal (or its authors) actually provides Green OA!

(2b) At the article level, "Green" means that the article has actually been made Green OA.

Apart from that one point, the Miguel et al article contains informative and useful between-journal data on Green and Gold OA, across fields and geographic areas.

It is only one of Miguel et al’s conclusions – that their between-journal data showing that Green OA journals have higher impact factors than both Gold OA and Gray journals somehow explain or invalidate the many within-journal studies demonstrating that Green OA articles within the same journal have higher citation counts than non-OA articles – that does not follow from the evidence (and cannot follow, methodologically or logically).

Björk B-C, Welling P, Laakso M, Majlender P, Hedlund T, et al. (2010) Open Access to the Scientific Journal Literature: Situation 2009. PLOS ONE 5(6): e11273

Gargouri, Y., Hajjem, C., Lariviere, V., Gingras, Y., Brody, T., Carr, L. and Harnad, S. (2010)Self-Selected or Mandated, Open Access Increases Citation Impact for Higher Quality Research PLOS ONE 5 (10)

Harnad, S. (2010a) The Immediate Practical Implication of the Houghton Report: Provide Green Open Access Now. Prometheus 28 (1). pp. 55-59.

Houghton, J.W., Rasmussen, B., Sheehan, P.J., Oppenheim, C., Morris, A., Creaser, C., Greenwood, H., Summers, M. and Gourlay, A. (2009). Economic Implications of Alternative Scholarly Publishing Models: Exploring the Costs and Benefits, London and Bristol: The Joint Information Systems Committee (JISC)

Hitchcock, S (2011) "The effect of open access and downloads ('hits') on citation impact: a bibliography of studies"

Swan, A (2010) "The Open Access citation advantage: Studies and results to date"

Wagner, B (2010) Open Access Citation Advantage: An Annotated Bibliography Issues in Science and Technology Librarianship 60

Swan, A. (2010) The Open Access citation advantage: Studies and results to date. Technical Report. School of Electronics & Computer Science, University of Southampton.

Abstract: This paper presents a summary of reported studies on the Open Access citation advantage. There is a brief introduction to the main issues involved in carrying out such studies, both methodological and interpretive. The study listing provides some details of the coverage, methodological approach and main conclusions of each study.

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Added Mar 15 2010
See also (thanks to Peter Suber for spotting this study!):

Wagner, A. Ben (2010) Open Access Citation Advantage: An Annotated Bibliography. Issues in Science and Technology Librarianship. 60. Winter 2010

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I'd suggested that these studies are clearly ripe for a meta-analysis:

On Mar 12, 2010 Gene V Glass wrote the following:

"Far more issues about OA and meta analysis have been raised in this thread for me to [be able to] comment on. But having dedicated 35 years of my efforts to meta analysis and 20 to OA, I can’t resist a couple of quick observations.

Holding up one set of methods (be they RCT or whatever) as the gold standard is inconsistent with decades of empirical work in meta analysis that shows that “perfect studies” and “less than perfect studies” seldom show important differences in results. If the question at hand concerns experimental intervention, then random assignment to groups may well be inferior as a matching technique to even an ex post facto matching of groups. Randomization is not the royal road to equivalence of groups; it’s the road to probability statements about differences.

Claims about the superiority of certain methods are empirical claims. They are not a priori dicta about what evidence can and can not be looked at."

Glass, G.V.; McGaw, B.; & Smith, M.L. (1981). Meta-analysis in Social Research. Beverly Hills, CA: SAGE.

Rudner, Lawrence, Gene V Glass, David L. Evartt, and Patrick J. Emery (2000). A user's guide to the meta-analysis of research studies. ERIC Clearinghouse on Assessment and Evaluation, University of Maryland, College Park.

Publications

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Update Jan 1, 2010: See Gargouri, Y; C Hajjem, V Larivière, Y Gingras, L Carr,T Brody & S Harnad (2010) “Open Access, Whether Self-Selected or Mandated, Increases Citation Impact, Especially for Higher Quality Research”
Update Feb 8, 2010: See also "Open Access: Self-Selected, Mandated & Random; Answers & Questions"

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Response to Comment by Ian Russell on Ann Mroz's 12 November 2009 editorial "Put all the results out in the open" in Times Higher Education:

It's especially significant that Ian Russell -- CEO of the Association of Learned and Professional Society Publishers (which, make no mistake about it, includes all the big STM commercials too) -- should be saying:

"It’s not 'lobbying from subscription publishers' that has stalled open access, it’s the realization that the simplistic arguments of the open access lobby don’t hold water in the real world... [with] open access lobbyists constantly referring to the same biased and dubious ‘evidence’ (much of it not in the peer reviewed literature)."

Please stay tuned for more peer-reviewed evidence on this, but for now note only that the study Ian Russell selectively singles out as not "biased or dubious" -- the "first randomized trial" (Davis et al 2008), which found that "Open access [OA] articles were no more likely to be cited than subscription access articles in the first year after publication” -- is the study that argued that in the host of other peer-reviewed studies that have kept finding OA articles to be more likely to be cited (the effect usually becoming statistically significant not during but after the first year), the OA advantage (according to Davis et al) is simply a result of a self-selection bias on the part of their authors: Authors selectively make their better (hence more citeable) articles OA.

Russell selectively cites only this negative study -- the overhastily (overoptimistically?) published first-year phase of a still ongoing three-year study by Davis et al -- because its result sounds more congenial to the publishing lobby. Russell selectively ignores as "biased and dubious" the many positive (peer-reviewed) studies that do keep finding the OA advantage, as well as the critique of this negative study (as having been based on too short a time interval and too small a sample, not even long enough to replicate the widely reported effect that it was attempting to demonstrate to be merely an artifact of a self-selection bias). Russell also selectively omits to mention that even the Davis et al study found an OA advantage for downloads within the first year -- with other peer-reviewed studies having found that a download advantage in the first year translates into a citation advantage in the second year (e.g., Brody et al 2006). (If one were uncharitable, one might liken this sort of self-serving selectivity to that of the tobacco industry lobby in its time of tribulation, but here it is not public health that is at stake, merely research impact...)

But fair enough. We've now tested whether the self-selected OA impact advantage is reduced or eliminated when the OA is mandated rather than self-selective. The results will be announced as soon as they have gone through peer review. Meanwhile, place your bets...

Brody, T., Harnad, S. and Carr, L. (2006) Earlier Web Usage Statistics as Predictors of Later Citation Impact. Journal of the American Association for Information Science and Technology (JASIST) 57(8) pp. 1060-1072.

Davis, PN, Lewenstein, BV, Simon, DH, Booth, JG, & Connolly, MJL (2008) Open access publishing, article downloads, and citations: randomised controlled trial British Medical Journal 337: a568

Harnad, S. (2008) Davis et al's 1-year Study of Self-Selection Bias: No Self-Archiving Control, No OA Effect, No Conclusion.

Hitchcock, S. (2009) The effect of open access and downloads ('hits') on citation impact: a bibliography of studies.

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Update Jan 1, 2010: See Gargouri, Y; C Hajjem, V Larivière, Y Gingras, L Carr,T Brody & S Harnad (2010) “Open Access, Whether Self-Selected or Mandated, Increases Citation Impact, Especially for Higher Quality Research”
Update Feb 8, 2010: See also "Open Access: Self-Selected, Mandated & Random; Answers & Questions"

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Five months after the fact, this week's Science Magazine has just published four letters and a response about Evans & Reimer's Open Access and Global Participation in Science, Science 20 February 2009: 1025.

You might want to also take a peek at these three rather more detailed critiques that Science did not publish...:

"Open Access Benefits for the Developed and Developing World: The Harvards and the Have-Nots"

"The Evans & Reimer OA Impact Study: A Welter of Misunderstandings"

"Perils of Press-Release Journalism: NSF, U. Chicago, and Chronicle of Higher Education"

Stevan Harnad
American Scientist Open Access Forum

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Update Jan 1, 2010: See Gargouri, Y; C Hajjem, V Larivière, Y Gingras, L Carr,T Brody & S Harnad (2010) “Open Access, Whether Self-Selected or Mandated, Increases Citation Impact, Especially for Higher Quality Research”
Update Feb 8, 2010: See also "Open Access: Self-Selected, Mandated & Random; Answers & Questions"

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Basken, Paul (2009) Fee-Based Journals Get Better Results, Study in Fee-Based Journal Reports. Chronicle of Higher Education February 23, 2009

(Re: Paul Basken) No, the Evans & Reimer (E & R) study in Science does not show that

"researchers may find a wider audience if they make their findings available through a fee-based Web site rather than make their work freely available on the Internet."

This is complete nonsense, since the "fee-based Web site" is immediately and fully accessible -- to all those who can and do pay for access in any case. (It is simply the online version of the journal; for immediate permanent access to it, an individual or institution pays a subscription or license fee.) The free version is extra: a supplement to that fee-based online version, not an alternative to it: it is provided for those would-be users who cannot afford the access-fee. In E & R's study, the free access is provided -- after an access-embargo of up to a year or more -- by the journal itself. In studies by others, the free access is provided by the author, depositing the final refereed draft of the article on his own website, free for all (usually immediately, with no prior embargo). E & R did not examine the latter form of free online access at all. (Paul Basken has confused (1) the size of the benefits of fee-based online access over fee-based print-access alone with (2) the size of the benefits of free online access over fee-based online-access alone. The fault is partly E & R's for describing their findings in such an equivocal way.)

(Re: Phil Davis) No, E & R do not show that

"the effect of OA on citations may be much smaller than originally reported."

E & R show that the effect of free access on citations after an access-embargo (fee-based access only) of up to a year or longer is much smaller than the effect of the more immediate OA that has been widely reported.

(Re: Phil Davis) No, E & R do not show that

"the vast majority of freely-accessible scientific articles are not published in OA journals, but are made freely available by non-profit scientific societies using a subscription model."

E & R did not even look at the vast majority of current freely-accessible articles (per year), which are the ones self-archived by their authors. E & R looked only at journals that make their entire contents free after an access-embargo of up to a year or more. (Cumulative back-files will of course outnumber any current year, but what current research needs, especially in fast-moving fields, is immediate access to current, ongoing research, not just legacy research.)

See: "Open Access Benefits for the Developed and Developing World: The Harvards and the Have-Nots"

Stevan Harnad
American Scientist Open Access Forum

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Update Jan 1, 2010: See Gargouri, Y; C Hajjem, V Larivière, Y Gingras, L Carr,T Brody & S Harnad (2010) “Open Access, Whether Self-Selected or Mandated, Increases Citation Impact, Especially for Higher Quality Research”
Update Feb 8, 2010: See also "Open Access: Self-Selected, Mandated & Random; Answers & Questions"

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Tenopir & King's confirmation of the finding (by Kurtz and others) -- that as more articles become accessible, more articles are indeed accessed (and read), but fewer articles are cited (and those are cited more) -- is best explained by the increased selectivity made possible by that increased accessibility:

The Seglen "skewness" effect is that the top 20% of articles receive 80% of all citations. It is probably safe to say that although there are no doubt some bandwagon and copycat effects contributing to the Seglen effect, overall the 20/80 rule probably reflects the fact that the best work gets cited most (skewing citations toward the top of the quality distribution).

So when more researchers have access to more (or, conversely, are denied access to less), they are more likely to access the best work, and the best work thereby increases its likelihood of being cited, whereas the rest correspondingly decreases its likelihood of being cited. Another way to put it is that there is a levelling of the playing field: Any advantage that the lower 80% had enjoyed from mere accessibility in the toll-access lottery is eliminated, and with it any handicap the top 20% suffered from inaccessibility in the toll-access lottery is eliminated too. Open Access (OA) allows all the cream to rise to the top; accessibility is no longer a constraint on what to cite, one way or the other.

(I would like to point out also that this "quality selectivity" on the part of users -- rather than self-selection on the part of authors -- is likely to be the main contributor to the citation advantage of Open Access articles over Toll Access articles. It follows from the 20/80 rule that whatever quality-selectivity there is on the part of users will be enjoyed mostly by the top 20% of articles. There is no doubt at all that the top authors are more likely to make their articles OA, and that the top articles are more likely to be made OA, but one should ask oneself why that should be the case, if there were no benefits [or the only benefit were more readers, but fewer citations!]: One of the reasons the top articles are more likely to be made OA is precisely that they are also the most likely to be used, applied and cited more if they are made OA!)

Stevan Harnad
American Scientist Open Access Forum