In many low and middle-income countries, adult mortality estimates are derived from surveys and censuses conducted through face-to-face interviews. These interviews can be time-intensive and are often impractical during health crises or humanitarian emergencies. The expansion in cellphone ownership and network coverage has created new opportunities for collecting demographic data through mobile phone surveys, but our understanding of selection biases and reporting errors of such data remains incomplete. This study reports on adult mortality estimates obtained through mobile phone surveys conducted in Burkina Faso, Malawi and the Democratic Republic of the Congo in 2021 and 2022. To mitigate respondent fatigue and network interruptions, we used a shortened version of the set of questions generally used in surveys to ask about the survival of respondents’ siblings. Mortality estimates obtained from mobile phone interviews were lower than those from face-to-face demographic surveys. Mortality rates from the mobile phone surveys were also approximately half those expected from World Population Prospects (WPP) estimates. We attribute this underestimation primarily to reporting errors, including inaccuracies in the ages and timing of sibling deaths collected through the shortened instrument. Coverage biases due to mobile phone ownership likely played a secondary role in the reduced mortality estimates. After imputing ages and dates based on full sibling histories collected in previous face-to-face surveys, mortality rates were more consistent with WPP and Demographic and Health Survey estimates. However, estimates would be improved with more accurate age at death and time of death reports. Mobile phone surveys offer a promising alternative for monitoring adult mortality in settings where face-to-face data collection is not feasible, but they seem to be susceptible to more frequent reporting errors.

age-specific mortality patterns, data quality, Demographic Health Surveys, direct estimation, health and security crises, low-and-middle-income countries, mobile phones, mortality, sample selection, surveys, under-five mortality