A growing reliance on the Internet as an information source when making choices about buying certain products raises the need for more research into electronic word of mouth. This study aims to contribute to the current scientific knowledge on how the valence of online reviews affects product performance. Using applications from the AppStore, we conduct an independent groups experiment to assess the mean changes in people’s evaluation of these apps as a result of online word-of-mouth. Furthermore, we add three moderating variables to analyze this relationship. The findings show that negative (positive) reviews have negative (positive) effects on app performance, and that the absolute size of the effect is larger when subjects are exposed to negative reviews (negativity effect). This study delivers contributions to both marketing research and marketing practice in that the results add to the current understanding of online WOM effects by showing in what way user reviews affect consumer behavior. Furthermore, a cross-sectional study has been conducted in the same category in the AppStore. The findings confirm the results from the experimental study.