I am looking for the percentage of total scholarly literature available in open access repositories by year of publication broken down by discipline.
I am aware of the following figure, however it is old. Are there any more recent statistics?
Swan, Alma. Policy guidelines for the development and promotion of open access. UNESCO, 2012.
As far as I see, to answer this question based upon a more recent data set one has to create the needed data set in advance.
The needed data set has to include all published articles, the publication year, the information of the access state on article level (gold/green) and a consistent classification.
One could start by using google scholar or the Thomson Reuters list to collect all published articles and repositories or a web trawler to find corresponding green open access versions. One could also use a data collector as BASE (Bielefeld Academic Search Engine). BASE offers browsing using the DDC which should help to identify the publications of the different disciplines, if one has no access to the Thomson Reuters list. Additionally, each article has an access state. The access state of an article can also be collected from oaDOI.
There are definitely several ways to get the needed information. Unfortunately, it seems that no one has done this work recently.