Martin, Tara G., Wintle, Brendan A., Rhodes, Jonathan R., Kuhnert, Petra M., Field, Scott A., Low-Choy, Samantha J., Tyre, Andrew J. & Possingham, Hugh P. (2005) Zero tolerance ecology: improving ecological inference by modelling the source of zero observations. Ecology Letters 8 (11), 1235-1246.R にはこのあたりの最尤推定計算やる zicounts なる package ある.