# 2. Sampling strategy

Wave 2 of the SHFS employed a multi‐stage stratified random sample, ensuring a sample representative of all sub‐populations of interest, while optimally balancing cost and precision of estimates. Strata were defined along two dimensions – administrative location (pre‐war regions and emerging states) and population type (urban areas, rural settlements, IDP settlements, and nomadic population), leading to a total of 57 strata (Table A.2). Sub‐populations in the urban centers of Mogadishu, Baidoa, and Kismaayo, in fisheries livelihood zones in coastal areas (Figure A.1), and IDP host communities were of particular interest and therefore deliberately oversampled.

The total planned sample size was 6,384 interviews, allowing for high‐precision consumption estimates with less than 10 percent relative standard errors for key sub‐populations and overall. The sample was allocated across strata following optimal (Neyman) allocation, minimizing the global sampling error of the consumption estimates (Neyman, 1934). Optimal allocation is given by where n� is the sample size in stratum _h, n_ is the total sample size, _H_ is the total number of strata, N� is the total population of stratum _h_ , _N_ is the total overall population, and S� is the standard deviation in stratum _h._ Hence, the number of households to be interviewed per stratum is mainly determined by the variability of consumption within the stratum ( S� ). S� was derived from the results of the SHFS Wave 1. The population size only matters for practical purposes in very small strata below 10,000 households. In the absence of a recent population census, the population of each stratum was derived from UNFPA’s 2014 Population Estimation Survey (PESS), which contains detailed estimates for each population type and administrative unit of interest.

The optimal allocation of interviews was subject to the following requirements:

- (i) 500 expected interviews in IDP settlements and 500 in nomadic populations;

- (ii) At least 600 interviews expected per administrative unit;

- (iii) Oversampled populations with

- Mogadishu (urban): 900 interviews, including IDPs;

- Kismaayo (urban) and Baidoa (urban): at least 500 interviews each;

- Coastal fisheries livelihood zones: at least 300 interviews;

- IDP host communities: 500 expected interviews.

Households are clustered into enumeration areas (EAs), with 12 interviews expected for each selected EA. A larger number of households per enumeration area would only marginally benefit the statistical estimation of indicators because of potential homogeneity among households in geographic proximity. A smaller number of households would result in fewer than 3 observations for each of the four optional modules capturing household consumption based on the Rapid Consumption Methodology, and thus affect the reliability of poverty estimates (see section 4).

The sampling design addressed the challenging security situation on the ground in two ways. First, a security assessment was conducted to exclude areas too dangerous for field teams to visit. Second, a micro‐listing approach was used in second‐stage sample selection to allow field teams to spend limited time on the ground. Replacement of sampling units during fieldwork followed a transparent and 5