Which Brands Gain Share from Which Brands? Inference from Store-Level Scanner Data

Market share models for weekly store-level data are useful to understand competitive structuresby delivering own and cross price elasticities. These models can however not be used toexamine which brands lose share to which brands during a specific period of time. It is for thispurpose that we propose a new model, which does allow for such an examination. We illustratethe model for two product categories in two markets, and we show that our model has validity interms of both in-sample fit and out-of-sample forecasting. We also demonstrate how our modelcan be used to decompose own and cross price elasticities to get additional insights into thecompetitive structure