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Abstract
This study examines how survey mode influences self-reported Water, Sanitation, and Hygiene (WaSH) outcomes, focusing on social desirability bias as a key mechanism. Using a randomized controlled trial (RCT) in Ethiopia’s North Wollo zone, we compare phone-based and face-to-face survey responses. Our findings reveal that Phone survey group has reported significantly higher rates of improved water access by 9.3 percentage points, improved sanitation facilities by 27.5 percentage points, and increased hand washing frequency by 0.96 times higher, compared to In-person respondents. These differences are consistent with increased social desirability bias in telephone surveys. Our findings remain robust to individual enumerator effects. We investigated several alternative mechanisms including survey fatigue, enumerator-specific effects, and enumerator learning; finding no empirical support for these explanations. While we cannot exclude the possibility that effects stem from in-person enumerators' ability to verify respondent claims, the evidence suggests social desirability bias as the primary driver. Our findings highlight important methodological implications for development research and policy evaluation, emphasizing the need for adjustments in survey design to mitigate mode-induced measurement biases in WaSH-related studies.