Attrition and Follow-Up Rules in Panel Surveys: Insights from a Tracking Experience in Madagascar

Most longitudinal surveys recontact households only if they are still living in the same dwelling, producing very high attrition rates, especially in developing countries where rural–urban migration is prevalent. In this paper, we discuss the implications of the various follow-up rules used in longitudinal surveys in the light of an original tracking survey from Madagascar. This survey attempted in 2005 to search and interview all individuals who were living in the village of Bepako in 1995, the baseline year of a yearly survey, the Rural Observatories. The tracking survey yielded an individual recontact rate of 78.8 percent, more than halving attrition compared to a standard dwelling-based follow-up rule. The tracking reveals a very high rate of out-migration (38.8 percent) and household break-ups, as three-quarters of recontacted households had divided between 1995 and 2005. The average income growth of the sample over the period increases by 28 percentage points when follow-up is extended to those who moved out of their household or village, suggesting that dwelling-based panels give a partial view of the welfare dynamics of the baseline sample. A higher baseline income per capita is associated with a higher probability of staying in Bepako and of being found in the tracking if one moved out. The hardest people to find are the poorest and most isolated. Special attention should be paid to collecting data that enable the identification and follow-up of individuals, without which attrition is likely to remain a source of bias even after a tracking procedure is carried out.