Based on a randomized survey experiment that was implemented in Malawi, the study finds that observationally‐equivalent, as well as same, households answer the same questions differently depending on whether they are interviewed with a short questionnaire or its longer counterpart. Statistically significant differences in reporting emerge across all topics and question types. In proxy‐based poverty measurement, these reporting differences lead to significantly different predicted poverty rates and Gini coefficients. The difference in poverty predictions ranges from 3 to 7 percentage points, depending on the model specification. A prediction model based only on the proxies that are elicited prior to the variation in questionnaire design yields identical poverty predictions irrespective of the short‐versus‐long questionnaire treatment. The results are relevant for estimating trends with questionnaires exhibiting inter‐temporal variation in design, impact evaluations administering questionnaires of different length and complexity to treatment and control samples, and development programs utilizing proxy‐means tests for targeting.