The power of the interviewer

African censuses and surveys remain dependent on interviewers for data collection with data quality assured through training and supervision. Many survey concepts and definitions are difficult to translate into African languages and some, such as the household, may have multiple criteria (sleeping, eating together and recognising an authority) which may not be fulfilled by everyone leading interviewers to prioritise different criteria. Some questions introduce unfamiliar ideas which may require considerable explanation by interviewers in order to obtain acceptable answers. Using published definitions, enumerator manuals and qualitative interview data with interviewers, supervisors, trainers, survey organisers and analysts in Tanzania, Uganda, Senegal and Burkina, we identify key areas where interviewer judgement plays a significant role in determining who is included or excluded from household surveys, or in shaping responses to certain questions. Interviewers take their responsibilities seriously but their preconceptions and interpretations have consequences for data reliability and harmonisation goals.