Omid Rafieian studies digital marketplaces and personalization, with a particular focus on understanding the determinants of consumer behavior. Consumers rely more on their smartphones and are exposed to increased numbers of ads and other notifications. In studying user responses to mobile aps, where ads are shown in a sequence, Rafieian and his co-authors measure the causal impact of the increase in variety of ads on users’ responses to the next ad. Consistent with psychological data, they find that if variety is increased, user attention is stimulated and engagement with the subsequent ad is increased.