The identification of age, cohort (vintage), and period (year) effects
in a panel of individuals or other units is an old problem in the social
sciences, but one that has not been much studied in the context of
measuring researcher productivity. In the context of a semi-parametric
model of productivity where these effects are assumed to enter in an
additive manner, we present the conditions necessary to identify and
test for the presence of the three effects. In particular we show that
failure to specify precisely the conditions under which such a model is
identified can lead to misleading conclusions about the productivity-age
relationship. We illustrate our methods using data on the publications
1986-1997 by 465 French condensed matter physicists who were born
between 1936 and 1960.
Key words: scientific productivity, age, identification, panel data, bibliometrics.
J.E.L. Classification: C23; O31; J44
UNU-MERIT Working Papers ISSN 1871-9872