In this paper we propose a simple method to measure the impact of promotional activities on weekly market share. The main idea is to assume that if promotion has an effect, it generates an additive outlier or a temporary level shift in the market share data. We propose an outlier robust...

Market share models for weekly store-level data are useful to understand competitive structures by delivering own and cross price elasticities. These models can however not be used to examine which brands lose share to which brands during a specificperiod of time. It is for this purpose that we...