Change PIM Definitions

The multi-strata model of Brownie et al. (1993) and Hestbeck et al. (1991) allows animals to move between strata with transition probabilities. These models are an extension of the Cormack-Jolly-Seber model (CJS) (Cormack 1964, Jolly 1965, Seber 1965) live recapture model extended to multiple areas or strata. A multi-strata model with live and dead encounters can also be fitted in MARK, as well as the robust-design multi-strata model. In all the multi-strata models, the transition probability, psi, is the probability of tranferring from one strata to another, with one transition being to remain in the current stratum. The sum of these transition probabilities must equal 1. Therefore, 1 less psi is estimated than is actually in the model, with the remaining psi estimated as the 1 - the sum of the remaining psi estimates.

The Change PIM Definitions allows the user to select which of the psi estimates is obtained by subtraction. The default model is to estimate the probability of remaining in the strata as the value obtained by subtraction. However, some models require constraints to be placed on the probability of remaining in the current stratum, which cannot be done if this value is obtained by subtraction. Therefore, this menu choice allows the user to select which transition probability is obtained by subtraction. This menu choice works with all multi-strata models, including the multi-strata model with live and dead encounters and the robust-design multi-strata model.

Care must be taken when model averaging real parameter estimates to be sure that the same parameter is model averaged across all models. That is, MARK does not protect you from model averaging psi A to A and psi A to B if both are defined in different models as the first transition probability.