  Productivity is the quintessential indicator of efficiency in any production
system. It seems it has become a norm in bibliometrics to define research
productivity as the number of publications per researcher, distinguishing it
from impact. In this work we operationalize the economic concept of
productivity for the specific context of research activity and show the limits
of the commonly accepted definition. We propose then a measurable form of
research productivity through the indicator "Fractional Scientific Strength
(FSS)", in keeping with the microeconomic theory of production. We present the
methodology for measure of FSS at various levels of analysis: individual,
field, discipline, department, institution, region and nation. Finally, we
compare the ranking lists of Italian universities by the two definitions of
research productivity.
