In 2009, an experiment was conducted on 400 monographs, measuring the effects of Open Access (OA) on discovery, online consultation, sales figures, dissemination channels and citations (Snijder, 2010). In line with expectations, the experiment found that making books freely available enhances discoverability and online consultation. Furthermore, no significant influence on sales could be established.In October 2014 citations and tweets of the 400 monographs included in the original experiment were measured again.In 2009, it was not possible to assess whether making monographs freely available enhanced scholarly impact, nor could anything be said about influence on society at large. This paper revisits the experiment, drawing on additional citation data that has become available during an extended period of online availability of the monographs, as well as developments in the altmetrics landscape. It focuses its altmetrics analysis on tweets only, attempting to answer the following research question: does Open Access have a positive influence on the number of citations and tweets a mono-graph receives, taking into account the influence of scholarly field and language? The correlation between monograph citations and tweets is also investigated.

On 6 April 2016 the data file has been replaced by a corrected version. This new file is titled ‘Citations_Altmetrics_OA_books_Dataset_20150721’.

The previously published data file contained errors due to a mistake in sorting of the data. Because of this several columns on the right side of the table did not correspond to the correct cells in the columns to the left. This original data file is no longer available.