low income, there are five lower middle and four upper middle income countries in the mix as well. Finally, four countries are classified as fragile and conflict-affected situations.<sup>15</sup> There is significant cross-country variation in unit costs. While the average unit cost is about USD 170, the unit costs range from USD 36 to nearly USD 360. Some of the cost patterns are instructive: for example, surveys in sub-Saharan Africa tend to be more expensive, while in three of the four fragile countries unit costs are lower than the average. Since we do not have actual survey implementation costs per household for all 78 countries of interest, to estimate the total costs of implementing 390 surveys over the period of 2016-2030, we would need to compute average costs from our sample of 18 surveys. The divergent costs across surveys suggest that the method for calculating the average (by region, income group or fragility) will have a stated impact on the total cost estimates. Furthermore, the large disparity in unit costs suggests the importance of gathering detailed information from more countries. Currently, there is no representation from small island countries, and Europe and Central Asia and East Asia and Pacific are represented by only one country. If we restrict our focus to the estimation of survey implementation costs for IDA and IDA/IBRD blend countries, this is less problematic. However, once we expand this costing exercise to all countries facing data gaps, the lack of data on unit costs from small island countries could cause a potential bias in our estimates.

# **b. Sample size formulation for implementation cost projections**

The sample size of household surveys is another important determinant of survey implementation costs. According to our database, the sample size of the household surveys varies largely from slightly under 3,000 (Uganda 2009/10) to around 27,000 (Peru 2014). The average survey size is about 11,000 households and the median is 9,000. While the required sample size can differ significantly across countries, for the current exercise, we use a normative sample of 7,000 households. The sample size of 7,000 households within a two-stage cluster sampling framework is envisioned to yield poverty and inequality statistics at national- and five to ten sub-national(regional) levels. The sample size is multiplied by the unit cost associated for each of the 78 countries and the number of surveys to be conducted by each country over the 15-year period (i.e. 5 surveys) while defining the total implementation budget envelope. Since the reliability of the estimates depends on the variability of consumption or income data in each country, the robustness of the survey implementation cost estimates is also assessed under alternative sample sizes of 5,000, 9,000 and 11,000.<sup>16</sup>

> 15 - The list of “fragile situations” is available at: <u>http://siteresources.worldbank.org/EXTLICUS/Resources/511777 1269623894864/FY15FragileSituationList.pdf. We refer to fragile and conflict-affected situations as “fragile states”</u> or “fragile countries.”

> 16 The World Bank Household Survey Strategy notes that larger countries would consider larger sample size to produce statistics at the sub-state level. For small area statistics, the use of model-based estimates could be promoted as an alternative to increased sample sizes.

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