Doctor's visits. Winkelmann (2004) fits a Poisson model to explain the number of doctor's visits using panel data drawn from the GSOEP from 1995-1999. The explanatory variables include, age, age-squared, dummy for male, years of education, dummy for married, household size, active sports, good health, bad health, whether on social assistance, \(\log\) (income), yearly dummies, whether self-employed, full-time, part-time, or unemployed, and quarterly dummies. The data set can be downloaded from the Journal of Applied Econometrics archive web site: (http://qed.econ.queensu.ca/jae/).

(a) Run the Poisson random and fixed effects regressions given in Table II on page 466 of Winkelmann (2004). How does being married or being on welfare affect the number of doctor's visits?

(b) Run the Negative Binomial random and fixed effects regressions. How does \(\log\) (income) affect the number of doctor's visits?