Assessment of a gridded population sample frame for a household survey of refugee populations in Uganda, 2021

To date, few HIV-related population-based data are available for refugee populations. Household surveys typically require reliable population counts and well-defined geographic areas, which are often not available for refugee settlements. We describe the gridded population sampling approach as an option for conducting such a survey in Uganda and describe its application for a household survey in Uganda and assess its utility among refugee populations.

The Uganda Refugee Population-based HIV Impact Assessment (RUPHIA) 2021 was a cross-sectional, population-based HIV survey among refugee households in Ugandan settlements, excluding Kampala. We collected shapefiles and population counts for the refugee settlements. These shapefiles from the various geographic areas of interest represented the aggregated refugee settlement zones (including all settlements with available zone shapefiles) and served as the base for creating the sample frame. The sample frame was constructed by disaggregating United Nations High Commission for Refugees population counts from large refugee settlement zones into 100 × 100 m grid cells using WorldPop's peanutButter-Disaggregate app that uses building footprint information to distribute the population into the grid cells. We then utilized a gridded population sampling approach which redistributed the population into manageable-sized areas of contiguous grid cells based on their estimated population size, forming enumeration area-like sampling units using the publicly available GridEZ algorithm.

The resulting gridded population dataset had 43,193 100 m x 100 m cells with an estimated mean of 31 people per cell and a range from 2 to 1028. The final gridded population sample frame had 2636 GridEZ units with an average population of 500 ranging from 178 to 1531. The sample frame performed well for survey activities, with few issues encountered in the field, although the size measures for number of households had some inaccuracies, due to issues such as compounds having multiple structures.

Gridded population sampling was successfully utilized for this refugee study, saving time and money that would have been needed if enumeration of all the refugee settlements had been required. Gridded population sampling is a useful tool when census data are outdated or unavailable or when the population is dynamic, such as with refugees or other mobile or at-risk populations for surveillance or as part of a humanitarian response.