Zero Augmentation: A method for fitting zero-modified count models that allows both zero-inflation and zero-deflation

Abstract

The concept of zero-inflation is now well established, and several software packages exist that fit zero-inflated models. Whilst there is some mention of zero-deflation in the literature, there is very little published evidence of research into zero-modified models that allow for both zero-inflation and zero-deflation within the one model. We present a very simple method that enables the fitting of zero-modified models via any software that fits zero-inflated models, and investigate the benefits of fitting zero-modified models.