Hi, I am hoping to get some clarity on a widely used reference related to the consequences of violating closure in a robust design model. Section 15.5 in the Mark manual discusses the assumptions of the RD model and says:

"If movement in and out of the study area is completely random during the period, then the estimator for p∗i remains unbiased." and the 1999 Kendall paper is referenced.

I've read the Kendall paper and have some doubts whether this is true. Figure 1 in the paper shows two scenarios and in a) movement into and out of the study area happens throughout the secondary occasions. Kendall says "In this case, the probability of being in the study area is at best confounded with capture probability" and then in the discussion he says "...although completely random emigration does not introduce bias to estimators for parameters associated with the superpopulation, the probability of temporary emigration is confounded with capture probability if it occurs at the same temporal scale as sampling."

If capture probability is confounded with temporary emigration how can p* be unbiased? I'm trying to resolve this apparent contradiction, especially since I know Kendall wrote the RD chapter in the Mark manual and so is unlikely to have gotten the reference wrong. Also, it seems to me that scenario a) in the paper is the more general situation whereas b) applies to quite specific situations.

Many thanks

Greg