Well done! Your last preprint in PeerJ is very interesting. Note our study about Gold OA in the last issue of Scientometrics:
Dorta-González, P., González-Betancor, S. M., & Dorta-González, M. I. (2017). Reconsidering the gold open access citation advantage postulate in a multidisciplinary context: an analysis of the subject categories in the Web of Science database 2009–2014. Scientometrics 112 (2), 877-901
This is a very interesting and informative article. I'd like to make a few points about your definitions though.
1) In your bulleted list in the Literature Review section, you don't mention that gold OA involves immediate open access to the article. I think this is an important part of the definition.
2) In your list of definitions in the Methods > OA determination section you seem to be mixing categories. "Gold" refers to an article published under certain conditions (i.e. immediate OA from a publisher with re-use rights). Such an article may appear in a pure OA journal or in a hybrid. "Hybrid" is a type of journal (in which some articles are gold OA and others are paywalled), not a type of article. There is no inherent difference between a gold article appearing in a hybrid and a gold article appearing in an OA journal. They both have the same characteristics; they just appear in different venues.
Very nice work! There has also been interesting research demonstrating the amplification effects of open access to broader society via channels like Wikipedia.
Teplitskiy, M., Lu, G. and Duede, E. (2016), Amplifying the impact of open access: Wikipedia and the diffusion of science. Journal of the Association for Information Science and Technology. doi:10.1002/asi.23687
Thanks for a really interesting piece of work. The trends that you see across time and disciplines are encouraging, and it looks like your approach could be very valuable for studying how access to content progresses in the future. Given the different approaches to OA that are being taken in different parts of the world, I wonder if geographic trends could be studied using the resources that you’ve developed. Here are a few specific comments for consideration.
1) I was puzzled by the data in Figure A4 about licenses. You say that you only found a license on 14.8% of the open access articles. Does this mean that there was no license information at all on the bulk of the articles or that you weren’t able to detect a license? Maybe the problem is the lack of consistency in the way that publishers present this information. Either way, I think this might be better presented and discussed as part of the main text, given that the number seems very low. Also given that ‘having no license’ is a criterion for your bronze category, it could be that this category looks much bigger than it really is.
2) If a fully OA journal is not indexed by DOAJ but does use a CC license, where would that content end up in your categorisation? I wasn’t sure if your gold OA category requires the journal to be indexed in DOAJ. Might be worth clarifying.
3) Hybrid. As I understand it, I think this category might also include some delayed OA articles, where those articles are published with a license. An example is Rockefeller University Press who release all content after 6 months (unless the author pays for immediate OA), and use a CC-BY-NC-SA license for this delayed free access (http://www.rupress.org/content/permissions-and-licensing). I’m not sure how many other publishers combine delayed free access with a CC license. Again, might be worth mentioning.
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