  As uptake among researchers is constantly increasing, social media are
finding their way into scholarly communication and, under the umbrella term
altmetrics, were introduced to research evaluation. Fueled by technological
possibilities and an increasing demand to demonstrate impact beyond the
scientific community, altmetrics received great attention as potential
democratizers of the scientific reward system and indicators of societal
impact. This paper focuses on current challenges of altmetrics. Heterogeneity,
data quality and particular dependencies are identified as the three major
issues and discussed in detail with a particular emphasis on past developments
in bibliometrics. The heterogeneity of altmetrics mirrors the diversity of the
types of underlying acts, most of which take place on social media platforms.
This heterogeneity has made it difficult to establish a common definition or
conceptual framework. Data quality issues become apparent in the lack of
accuracy, consistency and replicability of various altmetrics, which is largely
affected by the dynamic nature of social media events. It is further
highlighted that altmetrics are shaped by technical possibilities and depend
particularly on the availability of APIs and DOIs, are strongly dependent on
data providers and aggregators, and potentially influenced by technical
affordances of underlying platforms.
