  Differences between the impacts of Open Access (OA) and non-OA research have
been observed over a wide range of citation and altmetric indicators, usually
finding an Open Access Advantage (OAA) within specific fields. However,
science-wide analyses covering multiple years, indicators and disciplines are
lacking. Using citation counts and six altmetrics for 38.7M articles published
2011-21, we compare OA and non-OA papers. The results show that there is no
universal OAA across all disciplines or impact indicators: the OAA for
citations tends to be lower for more recent papers, whereas the OAAs for news,
blogs and Twitter are consistent across years and unrelated to volume of OA
publications, whereas the OAAs for Wikipedia, patents and policy citations are
more complex. These results support different hypotheses for different subjects
and indicators. The evidence is consistent with OA accelerating research impact
in the Medical & Health Sciences, Life Sciences and the Humanities; that
increased visibility or discoverability is a factor in promoting the
translation of research into socio-economic impact; and that OA is a factor in
growing online engagement with research in some disciplines. OAAs are therefore
complex, dynamic, multi-factorial and require considerable analysis to
understand.
