designated as the ‘parent’ household and the others as ‘split-off’ households.<sup>6</sup> For example, consider a husband and wife cohabiting in round 1, but who are now living in separate households in round 2. The parent household will typically be the one occupying the same dwelling as in round 1 or the household in a dwelling nearest the location of the round 1 dwelling. The other household(s) would be designated as a split-off household(s). The split-off households are then, ideally, tracked and interviewed in their new location. Often the designation between the two is somewhat arbitrary and one of convenience for field work.

Again, due to cost and logistics considerations, it may not be possible to track all split-off households. In this case, eligible movers are stratified and a sub-sample is selected for tracking. It is necessary to integrate this selection into the weight calculations. The rules on which movers to track need to be established (and well-enforced) based on the expected analytical primary uses of the data.

For example, in the Tanzania National Panel Survey (TZNPS), all regular adult household members were deemed as eligible tracking targets. This excluded children under the age of 15, servants, and guests. In the Ugandan National Panel Survey (UNPS), two households within each EA were randomly assigned to have all split-offs tracked, regardless of the age of the member who resided in a new household. Since this selection was done _ex ante_ at the statistics bureau headquarters, it was possible that some households selected for tracking did not have any members who formed a split-off, or that no one from the household was located in round 2.

In the TZNPS, there are no additional calculations necessary at this step because the tracking rules were defined at the individual level and therefore all households were eligible for tracking. In the UNPS, the sub-sampling of households complicates the weighting calculations. Ideally, the parent household would receive a tracking weight of 1, because it is selected into the sample with certainty. The weight for splitoff households that are subsampled to be followed would include a weight factor to account for the probability of selection into tracking. For the example of an EA with 10 households, this tracking probability would be 2/10. The appropriate expansion factor for each split–off that was tracked would −1 then be ~~�~~ 10<sup>2</sup> � or 5.

The uncertainty arises, however, from the fact that the difference between a parent and a split-off is a somewhat arbitrary distinction, driven mostly by location. As noted above, among the set of households in round 2 with members from the same round 1 household, the parent household is typically the one whose dwelling is in the same location as in round 1. This would mean if one child remained at the original location and the other five family members moved to another location, the child would be the parent household and the other five members the split-off.<sup>7</sup> If only the child re-located, the five original members would be the parent and the child the split-off. The designation becomes even more arbitrary if there are no members present in the original dwelling. In this case, field supervisors could choose to designate the parent household based on the number of original members, the location of the household head, or some other criteria.

Since the designation is to a great extent arbitrary, there should be no mathematical difference in the probability of selection between the parent and the split-off household. The probabilities of selection are therefore pooled and averaged over all households originating from a single original household. Consider

> 6 Note that ‘parent’ household does not literally refer to familial relationships, as the split-offs may themselves contain parents of members in the ‘parent’ household.

> 7 This also assumes that children are eligible tracking targets, as they are in the case of the UNPS.  If the same case had arisen in Tanzania, where children under 15 are not eligible tracking targets, the remaining child would not be counted.  Since all eligible household members had relocated, the entire household would be considered to have relocated.  The new location would be considered the parent household and there would be no split-offs in this case.

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