It is argued that the estimation techniques used by previous researchers to study rivalry in financial markets are inappropriate. The assumptions of both ordinary least-squares and Tobi analysis are violated when these techniques are used to analyze mobility and turnover data. To overcome the difficulties in the previous studies, we suggest a non-linear model (which is closely related to the Poisson model). This model is designed for describing frequency data and is not subject to the criticisms to which ordinary least-square and Tobut are subject.