  The evaluation of performance at the individual level is of fundamental
importance in informing management decisions. The literature provides various
indicators and types of measures, however a problem that is still unresolved
and little addressed is how to compare the performance of researchers working
in different fields (apples to oranges). In this work we propose a solution,
testing various scaling factors for the distributions of research productivity
in 174 scientific fields. The analysis is based on the observation of
scientific production by all Italian university researchers active in the hard
sciences over the period 2004-2008, as indexed by the Web of Science. The most
effective scaling factor is the average of the productivity distribution of
researchers with productivity above zero.
