Carsten Nieder, Astrid Dalhaug, and Gro Aandahl have published "Correlation between Article Download and Citation Figures for Highly Accessed Articles from Five Open Access Oncology Journals" in SpringerPlus.
Here's an excerpt:
Different approaches can be chosen to quantify the impact and merits of scientific oncology publications. These include source of publication (including journal reputation and impact factor), whether or not articles are cited by others, and access/download figures. When relying on citation counts, one needs to obtain access to citation databases and has to consider that results differ from one database to another. Accumulation of citations takes time and their dynamics might differ from journal to journal and topic to topic. Therefore, we wanted to evaluate the correlation between citation and download figures, hypothesising that articles with fewer downloads also accumulate fewer citations. Typically, publishers provide download figures together with the article. We extracted and analysed the 50 most viewed articles from 5 different open access oncology journals. For each of the 5 journals and also all journals combined, correlation between number of accesses and citations was limited (r=0.01-0.30). Considerable variations were also observed when analyses were restricted to specific article types such as reviews only (r=0.21) or case reports only (r=0.53). Even if year of publication was taken into account, high correlation coefficients were the exception from the rule. In conclusion, downloads are not a universal surrogate for citation figures.