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.