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Abstract:
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Measuring the causal impact of an advertising campaign on sales is an essential task for advertising companies. Challenges arise when companies run advertising campaigns in multiple stores which are spatially correlated, and when the sales data have a low signal-to-noise ratio which makes the advertising effects hard to detect. This paper proposes a novel Bayesian method to detect weaker impacts by comparing two posterior distributions of a latent variable—one obtained by using the observed data from the test stores and the other one obtained by using the data from their potential outcomes. A multivariate structural time series model is used to conduct the analysis. We capture the spatial correlation between stores through placing a G-Wishart prior on the precision matrix. Control stores are selected using an Expectation-Maximization variable selection method. To prevent the prediction intervals from being explosive, a stationarity constraint is imposed on the local linear trend of the model through a recently proposed prior. A detailed simulation study shows the effectiveness of using our proposed method to detect weaker causal impact. The new method is applied to a real dataset.
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