Tracking dwellings instead of households is a simpler option. Following up with households over time requires defining which household is the successor of the original household, which is not a trivial task, as households may split or regroup over time. As noted by Witoelar (2011) household membership and composition quickly change, household structure and boundaries are often unclear, and the definition of household often varies according to the objective of the survey. Continuity rules to define which household is regarded to be the continuation of the one observed during the previous survey are proposed and discussed in Falorsi (2009).

The LSMS-ISA panel surveys have established practical rules to define which household to follow. The Ethiopia ESS, for instance, identifies the group of household members still living in the original dwelling as the original household. If the household moved away as a whole, it is tracked and re-interviewed if it is still residing within the Ethiopian border. If all household members left the country, the unit is dropped from the sample. If the household split, the portion of the household that moved with the member identified as the head of the household in the previous wave is tracked and interviewed. Similarly, the Nigeria GHS-Panel interviews household members found in the original dwelling and tracks households that moved outside of the dwelling but are still located in Nigeria. If the household splits, the original household is defined as the group of household members still residing with the head of the household from the previous round. If the original household head is not found, the original household is defined as the one comprising the largest number of original household members.

Panels of dwellings and households have the disadvantage that members who moved out of their baseline household are not part of the sample anymore, despite still being part of the population. The sample of the remaining members therefore will be less representative of the population at the present time as well as of the population evolving over time. However, as we will detail later in the paper, this lack of representativeness is mitigated because all LSMS-ISA surveys incorporate new individuals who have joined interviewed (and tracked) households, such as newborns or immigrants.

The loss of representativeness over time can be addressed by tracking original individuals. The extent to which individual tracking can mitigate representativeness issues depends on decisions regarding the characteristics of the tracking targets and the geographical scope of the tracking. Conceptually, deciding which individuals to track depends on the characteristics of the population that need to be represented over time. Aspirations of studies that focus on a specific subpopulation are different from LSMS-ISA panel surveys, which intend to describe the national population.

However, tracking all individual movers can be very expensive. The more ambitious the tracking goals (e.g., the greater the distance away from their original home that an individual must be tracked), the more that costs will increase. Generally, LSMS-ISA individual tracking targets are defined based on the individual’s age as well as on their relationship to the household head. Malawi, Tanzania, and Uganda track and follow up with movers that are biologically related to the household head, excluding therefore servants or guests at the time of the previous survey. Moreover, all three surveys impose a lower bound under which individuals moving out of the households are not tracked (12 years old in Malawi and 15 years old in Tanzania and Uganda).

The geographical scope of the tracking may also impact the representativeness of the panel survey in future rounds, if those individuals or households that move the farthest are also very different from others. How far to track is generally established based on administrative boundaries, geographic boundaries, or distance (Witoelar, 2011). Panel surveys that rely on local tracking only search for households in the same EAs or nearby. Distant tracking allows for tracking movers far away the original dwelling. Regardless of whether they track households 22