The OpCit project has for many years kept a list of studies up to date on whether or not there is a citation advantage for Open Access articles.
SPARC Europe then updated it in 2015 here: List of studies until 2015.
In 2010, a summary of all the studies to date was also published. SPARC Europe updated the lists of studies, some comparative details of their methodologies, and their findings. The summary of study results (until 2015) can be found here
This table summarises the findings
| Total number of studies until 2015 | 70 |
| Studies that found a citation advantage | 46 |
| Studies that found no citation advantage | 17 |
| Studies that were inconclusive, found non-significant data or measured other things than citation advantage for articles |
7 |
The OpCit project’s work was highly valued and SPARC Europe was pleased to continue to capture that value for users and to help share experience on citations and OA.
In 2016 SPARC Europe decided not to further update The Open Access Citation Advantage Service since the citation advantage evidence has now become far more common knowledge to our authors.