  This article introduces the Multidimensional Research Assessment Matrix of
scientific output. Its base notion holds that the choice of metrics to be
applied in a research assessment process depends upon the unit of assessment,
the research dimension to be assessed, and the purposes and policy context of
the assessment. An indicator may by highly useful within one assessment
process, but less so in another. For instance, publication counts are useful
tools to help discriminating between those staff members who are research
active, and those who are not, but are of little value if active scientists are
to be compared one another according to their research performance. This paper
gives a systematic account of the potential usefulness and limitations of a set
of 10 important metrics including altmetrics, applied at the level of
individual articles, individual researchers, research groups and institutions.
It presents a typology of research impact dimensions, and indicates which
metrics are the most appropriate to measure each dimension. It introduces the
concept of a meta-analysis of the units under assessment in which metrics are
not used as tools to evaluate individual units, but to reach policy inferences
regarding the objectives and general setup of an assessment process.
