Our final DPD model specification requires careful delineation of premodeling steps, including endogeneity, optimal lag length, stability, and variable selection. First, we explain the sources of endogeneity and show how our model deals with them explicitly. We need to accommodate two likely sources of endogeneity in the model: (1) endogenous regressors (price, ratings volume, ratings valence, and product update) and (2) unobserved app quality. Second, we describe how we tackle the optimal lag length and stability of the model as well as the variable selection. Finally, we discuss the model estimation strategy.