Shopping less with shopping lists: Planning individual expenses ahead of time affects purchasing behavior when online grocery shopping

How do shopping lists affect purchasing behavior? On the one hand, breaking down a shopping task into its subcomponents might increase predicted budget for the shopping trip and consequently increase the number of purchases made and dollars spent. On the other hand, a shopping list may function as a concrete action plan for the shopping task and decrease the number of purchases made and dollars spent. In two studies, participants were randomly assigned to make a shopping list for their next grocery trip or not make a list and then completed the shopping trip virtually without the shopping list (Study 1) or with the shopping list (Study 2), using a popular online grocery store website. Those who were induced to make a shopping list prior to shopping bought marginally (Study 1) or significantly fewer (Study 2) items in an online grocery trip and spent marginally less money (Study 1). Simply making an overall spending prediction did not have the same effect as writing an itemized shopping list (Study 2), and purchases in this condition did not differ from those in the control group. We also document descriptive information on frequency of use and beliefs about functionality of shopping lists.