Table 4 provides a summary of the funding needs under these assumptions by regions and lending categories. Sub-Saharan Africa and IDA countries explain the vast majority of the total estimated cost, 76 percent and 82 percent, respectively, which supports the World Bank’s commitment to supporting data production in the poorest countries. The total cost of technical assistance provision in all countries in support of a total of 390 surveys across the 15-year period of interest will be approximately **USD 253 million** , assuming a uniform technical assistance provision cost of USD 540,000 per survey that grows at the same rate as the survey implementation cost. **<mark>The total survey implementation and technical assistance costs amount to USD 945 million,</mark>** <mark>of which survey operation costs explain 73 percent.</mark> A main challenge of this estimation exercise is that for most of the 78 countries, actual unit cost estimates are not available and costs need to be imputed from our cost database of 18 countries. There are at least three approaches that could be used for the imputation of the unit costs. For our baseline estimates of USD 690 million for the cost of survey operations, we assumed that the unit cost of a country is the same as the regional average unit cost. A clear concern here is that East Asia and Pacific and Europe and Central Asia each have one actual unit cost estimate. Average unit costs can be calculated by country income classification as well. Finally, the average of all 18 countries could be chosen as the unit cost for all of the 78 countries.

Table 5 includes total survey implementation and technical assistance cost estimates based on 1) whether the region-specific, the income class-specific, and the global average unit cost is assigned to each of the 78 countries of interest; and 2) different assumptions on sample size (5,000; 7,000; 9,000; 11,000) and annual growth rate of unit costs (0 percent; 2 percent; 2.5 percent; 3 percent). Depending on the assumptions, the estimated total cost of survey operations varies from USD 371 million to over USD 1.1 billion. The median total cost of all the options presented in Table 5 is USD 695 million, coincidentally very close to the paper’s preferred estimate of USD 692 million. Using the income class-specific average unit costs or the global average unit cost that grow at an annual rate of 2.5 percent and interviewing 7,000 households per survey, the total survey implementation cost estimates decrease slightly to USD 651 million and USD 623 million, respectively. These changes are mainly driven by the fact that the average unit cost in sub-Saharan Africa is higher, and the region accounts for 39 of the 78 countries of interest.

Needless to say, these estimates based on different notions of average unit cost mask important details. For example, while assigning regional average unit costs to countries, we assume the same unit cost for Low Income (e.g., the Democratic Republic of Congo) and Lower Middle Income (e.g., the Republic of Congo) countries in the same region. On the other hand, assigning income class-specific average unit costs to countries implies that the unit cost in the Democratic Republic of Congo is the same as in Tajikistan and Haiti, as they are also Low Income countries. Mindful of these considerations, we still rely on regional averages for our baseline estimates to impute unit costs. This is a simple and transparent measure that captures regional heterogeneity in survey costs.

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