TY  - JOUR
AU  - Hausman,Jerry A.
AU  - Hall,Bronwyn H.
AU  - Griliches,Zvi
TI  - Econometric Models for Count Data with an Application to the Patents-R&D Relationship
JF  - National Bureau of Economic Research Technical Working Paper Series
VL  - No. 17
PY  - 1984
Y2  - October 1984
UR  - http://www.nber.org/papers/t0017
L1  - http://www.nber.org/papers/t0017.pdf
N1  - Author contact info:
Jerry A. Hausman
Department of Economics
MIT, Room E52-271A
50 Memorial Drive
Cambridge, MA  02139
Tel: 617/253-3644
Fax: 617/253-1330
E-Mail: jhausman@mit.edu

Bronwyn H. Hall
Dept. of Economics
549 Evans Hall
UC Berkeley
Berkeley, CA 94720-3880
Tel: 510/642-3878
Fax: 510/548-5561
E-Mail: bhhall@nber.org

Zvi Griliches
E-Mail: N/A user is deceased
AB  - This paper focuses on developing and adapting statistical models of counts (non-negative integers) in the context of panel data and using them to analyze the relationship between patents and R&D expenditures. The model used is an application and generalization of the Poisson distribution to allow for independent variables; persistent individual (fixed or random) effects, and "noise" or randomness in the Poisson probability function. We apply our models to a data set previously analyzed by Pakes and Griliches using observations on 128 firms for seven years, 1968-74. Our statistical results indicate clearly that to rationalize the data, we need both a disturbance in the conditional within dimension and a different one, with a different variance, in the marginal (between) dimension. Adding firm specific variables, log book value and a scientific industry dummy, removes most of the positive correlation between the individual firm propensity to patent and its R&D intensity. The other new finding is that there is an interactive negative trend in the patents - R&D relationship, that is, firms are getting less patents from their more recent R&D investments, implying a decline in the "effectiveness" or productivity of R&D.
ER  -