A CONSTRAINED COOK-JACOBSON MODEL OF VISIBILITY BIAS

A generalization of the Cook-Jacobson model for assessing closed popul ation size from aerial survey data is presented. Estimators for the nu mber of animal groups of a specific size and group sighting probabilit ies are developed, along with the corresponding variance estimators. E stimation is based on a log-linear model subject to linear and nonline ar constraints. Of particular interest are constraints that relate gro up size to the group sighting probabilities. A Wald test is presented for assessing the appropriateness of the proposed constraints. Substan tial reductions in variance estimates can be obtained for the constrai ned model when compared with variance estimates from the saturated or unconstrained Cook-Jacobson model.