  Alternative metrics are currently one of the most popular research topics in
scientometric research. This paper provides an overview of research into three
of the most important altmetrics: microblogging (Twitter), online reference
managers (Mendeley and CiteULike) and blogging. The literature is discussed in
relation to the possible use of altmetrics in research evaluation. Since the
research was particularly interested in the correlation between altmetrics
counts and citation counts, this overview focuses particularly on this
correlation. For each altmetric, a meta-analysis is calculated for its
correlation with traditional citation counts. As the results of the
meta-analyses show, the correlation with traditional citations for
micro-blogging counts is negligible (pooled r=0.003), for blog counts it is
small (pooled r=0.12) and for bookmark counts from online reference managers,
medium to large (CiteULike pooled r=0.23; Mendeley pooled r=0.51).
