specific LSMS-ISA Uganda National Panel Survey (UNPS) survey documentation, all individuals older than 15 years that are biologically related to the head of household who leave a sampled household are found and interviewed, as long as they do not move out of the parish where they are not tracked and their characteristics of interest are not recorded. However, referring again to were initially located. The latter rule implies that people who left their parish after time ttthe specific example, it is useful to note that regardless of the tracking rules, UNPS survey<sup>∗</sup> enumerators often track all those who remained within the Uganda border, even if they moved out of the original EA or parish. is re-contacted for the survey, the enumerator identifies all of their household members and collects the survey data. This ensures tt<sup>∗</sup> that the study captures changes in the household composition (due to births, deaths, marriages, Once an individual selected in the original sample SS . tt<sup>∗</sup> etc.) of all the individuals tracked in survey SS that were tt<sup>∗</sup> tt<sup>∗∗</sup> ←tt<sup>∗</sup> tt<sup>∗∗</sup> ←tt<sup>∗</sup> Thus, starting from the original sample SS , the longitudinal sample SS. of mm tt<sup>∗∗</sup> ←tt<sup>∗</sup> tt<sup>∗∗</sup> ←tt<sup>∗</sup> tt<sup>∗</sup> households with nn individuals is formed. SS contains all persons of SS Current time tracked, along with all members of their households at time tt<sup>∗∗</sup> are tracked and surveyed. The rules of tracking and data collection are the same as those tt<sup>∗∗</sup> tt<sup>∗∗</sup> ←tt<sup>∗</sup> tt. No new sample is selected. The SS and SS samples formed at the time tt<sup>∗∗</sup> sample. tt<sup>∗∗</sup> ←tt<sup>∗</sup> according to the specific survey’s tt<sup>∗</sup> already described for the formation of the SS longitudinal sample from the SS tt<sup>∗∗</sup> tt<sup>∗∗</sup> Thus, the enumerators track all nn individuals of sample SS ∩ tt←tt<sup>∗∗</sup> tt←tt<sup>∗∗</sup> tracking rules. This way, the enumerators form longitudinal sample SS , with mm and observed in longitudinal sample tt←tt<sup>∗∗</sup> tt<sup>∗</sup> households and nn people. Furthermore, the enumerators track all the people of SS tt<sup>∗∗</sup> ←tt<sup>∗</sup> tt<sup>∗</sup> SS who are the people selected in original sample SS people. tt<sup>∗∗</sup> ←tt<sup>∗</sup> tt←tt<sup>∗</sup> tt←tt<sup>∗</sup> tt←tt<sup>∗</sup> SS . So, the enumerators form longitudinal sample SS , with mm households and nn . tt←tt<sup>∗∗</sup> tt←tt<sup>∗</sup> The samples for the estimation at time tt are SS and SS

# 3.2. Movers and representativeness of the samples

Movers create two types of problems in longitudinal surveys. First, there are additional costs. Surveys that employ face-to-face interviews use cluster and multi-stage sampling designs to control costs. Following a mover to a new address may incur considerable extra expenses if the new address is not in one of the original sample areas. Also, there is a risk that no interviewer may be available to visit a mover if the move is discovered during the field operations. Thomas et al. (2001) discuss the cases of certain surveys in low-income countries that suffered significant attrition and bias because they did not track movers. Therefore, new contact information should be obtained to facilitate collecting data on the mover through phone or online interviewing. Another solution is to collect the data of interest on movers through proxy interviews; however, using proxies requires implementing adjustments in the estimation phase to reduce bias.

Based on the above, tracking protocols should be defined to determine a reasonable approach for balancing increased costs on one hand and distortion or bias on the other.

The target current population of households can be defined as the union of the three disjoint subpopulations: ∗ ∪E ∗∗ ∗ ∪E ∗∗ where tt tt←tt tt ←tt tt←tt (3.1) HH = FF 9