SIMPLE CAPTURE-RECAPTURE MODELS PERMITTING UNEQUAL CATCHABILITY AND VARIABLE SAMPLING EFFORT

We consider two capture-recapture models that imply that the legit of the probability of capture is an additive function of an animal catcha bility parameter and a parameter reflecting the sampling effort. The m odels are special cases of the Rasch model, and satisfy the property o f quasi-symmetry. One model is log-linear and the other is a latent cl ass model. For the log-linear model, point and interval estimates of t he population size are easily obtained using standard software, such a s GLIM.