Rayan H. M. Alkhawtani et al. have published "Citation Advantage for Open Access Articles in European Radiology" in .
Here's an excerpt:
The results of our study show that open access articles in European Radiology are significantly and independently more frequently cited than subscription access articles. This can be explained by the facts that open access by definition does not require a journal subscription or payment of a fee to read the article, open access offers potentially faster and easier article access even to subscribers because there is no need to login, and open access articles are also published in PubMed Central, which improves article visibility. Altogether, this may increase the number of article reads and subsequent citations.