In IDP strata, PPS sampling is applied at the IDP settlement level, determining how many enumeration areas are to be selected in each settlement. PSUs were drawn separately for each stratum, with at least 20 percent additional PSUs selected to serve as replacements in case one of the main PSUs needed to be replaced (see section 2).

# _Secondary sampling units (SSUs) and second‐stage sample selection_

Even in areas deemed accessible per the security assessment, it was critical to the safety of field staff and respondents that teams would spend as little time as possible in each EA. Himelein et al. (2016) discuss and compare several second‐stage sample selection strategies for use in contexts such as this one. In wave 2 of the SHFS, a micro‐listing approach is used in second‐ and final‐stage sample selection. In micro‐listing, enumeration areas are divided into smaller enumeration blocks. Rather than performing a time‐ consuming full listing of all households in the EA, enumerators list only households in one enumeration block, then select the household to be interviewed, and immediately conduct the interview, greatly reducing the time required in the EA.

Enumeration blocks were generated through different means, depending on the population type. In urban and rural strata, the EAs selected in the first stage were manually segmented into enumeration blocks (EBs) using satellite imagery from Google Earth or Bing, counting the number of structures visible in each. Enumeration blocks served as secondary sampling units (SSUs) in the sampling design. Enumeration blocks were created as per the following general criteria:

- <mark>Each selected EA would be comprehensively covered by enumeration blocks.</mark>

- <mark>Each EA would be delineated into 12 enumeration blocks, expecting one interview per block.</mark>

- <mark>Each enumeration block would contain at least 1 and at most 12 structures.</mark>

- <mark>Enumeration blocks in the same EA should have roughly the same number of visible structures.</mark>

- <mark>Blocks would be drawn to take account of natural boundaries.</mark>

- <mark>Each block should have a central point from which all structures in the block can be seen.</mark>

The general criteria for block delineation allow for several special cases:

- (i) If any PSU contained fewer than 12 structures, it would not be possible to delineate 12 blocks of the same size.

- (ii) If any PSU contained more than 150 structures, more than 12 blocks were delineated, following the above criteria.

- (iii) Given the design features of the sample, a fraction of PSUs was selected more than once. This occurred in two instances: First, given the nature of the first‐stage sample selection with PPS, very large PSUs were selected twice or three times. This was especially likely in strata with a relatively short list of PSUs and a relatively large number of required interviews in the stratum. Second, as outlined in the previous section, PSUs were selected more than once if they formed part of one of the oversamples. The number of required interviews and consequently the required number of enumeration blocks was scaled up proportionately in these cases. For instance, if a PSU was selected twice, 12*2=24 interviews and blocks were

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