Davis study still lacks self-selection control group (and the sample is still small)

[Philip Davis]

Stevan,
Your new interest in sample sizes implies -- although you don't seem 
willing to admit -- that an OA citation advantage is much, much smaller 
than initially reported.  Early studies (including yours) estimated the 
citation effect to be somewhere between 50% and 500% -- ranges that 
should be easily detectable with smaller sample sizes such as our 
study.  By focusing on the fact that I do not have the statistical power 
to detect very small differences is really an admission that an OA 
citation advantage -- if one truly exists -- can be largely explained by 
other theories (e.g. self-selection) and that the part attributable to 
free access is very small indeed.

--Phil Davis

Stevan Harnad wrote:
> Adminstrative info for SIGMETRICS (for example unsubscribe): 
> http://web.utk.edu/~gwhitney/sigmetrics.html
> On 2010-11-23, at 9:46 AM, Philip Davis wrote:
>
>> Critics of our open access publishing experiment (read: Stevan 
>> Harnad) have expressed skepticism that we were too eager to report 
>> our findings and should have waited between 2 and 3 years.  All of 
>> the articles in our study have now aged 3-years and we report [1] 
>> that our initial findings [2] were robust: articles receiving the 
>> open access treatment received more article downloads but no more 
>> citations.
>>
>> ARTICLE DOWNLOADS
>> During the first year of publication, open access articles received 
>> more than double the number of full-text downloads (119%, 95% C.I. 
>> 100% - 140%) and 61% more PDF downloads (95% C.I. 48% - 74%) from a 
>> third more unique visitors (32%, 95% C.I. 24% - 41%). Abstract views 
>> were reduced by nearly a third (-29%, 95% C.I. -34% - -24%) signaling 
>> a reader preference for the full article when available.
>>
>> ARTICLE CITATIONS
>> Thirty-six months after publication, open access treatment articles 
>> were cited no more frequently than articles in the control group 
>> (Figure 2). Open access articles received, on average, 10.6 citations 
>> (95% C.I. 9.2 -12.0) compared to 10.7 (95% C.I. 9.6 - 11.8) for the 
>> control group. No significant citation differences were detected at 
>> 12, 18, 24 and 30 months after publication.
>>
>>
>> 1. Davis, P. M. 2010. Does Open Access Lead to Increased Readership 
>> and Citations? A Randomized Controlled Trial of Articles Published in 
>> APS Journals. The Physiologist 53: 197-201. 
>> http://www.the-aps.org/publications/tphys/2010html/December/open_access.htm
>>
>> 2. Davis, P. M., Lewenstein, B. V., Simon, D. H., Booth, J. G., & 
>> Connolly, M. J. L. 2008. Open access publishing, article downloads 
>> and citations: randomised trial. BMJ 337: a568. 
>> http://dx.doi.org/10.1136/bmj.a568


-- 
Philip M. Davis, Ph.D.
Department of Communication
301 Kennedy Hall
Cornell University, Ithaca, NY 14853
email: pmd8 at cornell.edu
phone: 607 255-2124
https://confluence.cornell.edu/display/~pmd8/resume
http://scholarlykitchen.sspnet.org/author/pmd8/