Simulation parameters Average number of cases Type I error rates (%)
α σ   CPa/FEb GEEc
-5 1 488 4.0 4.3
  1.5 896 4.3 4.0
-6 1 179 3.7 4.0
  1.5 336 5.0 5.1
-7 1 66 4.4 4.3
  1.5 124 2.8 2.5
-8 1 25 6.2 6.0
  1.5 46 4.1 4.0
aCP, conditional Poisson model.
bFE, fixed effects model.
cGEE, generalized estimation equations.
Table 1: Type I error rates from 1000 simulations under the null hypothesis, β1=0, when individual-specific random coefficients have a normal distribution.