guish agricultural workers in parts of our analysis. Employed individuals are considered to be high-skilled workers if at the time of the survey they worked in any of the following occupation types: professional, clerical, skilled manual labor, sales, services, or agriculture (employee). Individuals were considered to be low-skilled workers if they worked in any of the following occupation types: domestic, unskilled manual labor, or agriculture (self-employed). Among the respondents in our data, 69.03 percent reported being employed, and 30.97 percent reported that they were not employed. Among skilled workers who in our data, the occupations were in the following categories: sales (38 percent); manual labor (18 percent) agricultural employee (16 percent); service-sector (12 percent); professional, technical or managerial occupations (12 percent); clerical occupations (2 percent). Among unskilled workers, 80 percent reported being self-employed in agriculture, and the remaining 20 percent were in either in domestic work or as unskilled manual laborers. Among respondents, 63 percent resided in rural areas, and 39 percent resided in urban areas. The ages of survey respondents were as follows: 25 or younger (39 percent), 25 to 50 (57 percent), over 50 (0.2 percent).

To look at the differential effects of investment in infrastructure across countries at different stages of development, we group the survey data into two categories of development. Using PPP-adjusted GDP per capita, we classify countries as less developed or more developed. A country is less developed if its PPP-adjusted GDP per capita falls below 2017 USD 3,400. In the LSMS, 97.37 percent are categorized as less developed. In the DHS, 64 percent of the countries are categorized as less developed.

# **3.3 Roads**

We combine geo-referenced household survey data with spatial data on road expansions as used by Berg et al. (2018) and Jedwab and Storeygard (2021).<sup>3</sup> The development of road infrastructure is tracked over 40 years from 1971 to 2014. Data on both the layout and road type are included, relying on layouts from Nelson and Deichmann (2004) and completed with information extracted from Michelin maps. The road-layout information used by Nelson and Deichmann (2004) was primarily constructed using information from the U.S. Digital Chart of the World database, originally constructed by the U.S. Defense Mapping Agency. Road surface information was obtained using 64 Michelin road maps for the northeast, northwest, and central-south regions of mainland sub-Saharan Africa. Roads are divided into the following categories: earth/dirt, paved, improved, or highway. We combine the last three of these categories into one ”main road” category. Michelin also collects statistics on road development projects, and its maps are meant to specify the year during which a specific road was made operational. However, Michelin maps for some states and time periods do not exist. Overall, the road network in Africa has steadily expanded from 239,018 km in 1971 to 334,391 km in 2014. Figure 1 depicts the evolution of main roads from 1971 to 2012. We combine the road network information with the geo-referenced households from the DHS. Overall, the mean distance of households from the main roads is 66 km in the DHS and 14.6 km in LSMS surveys.

> 3The roads digitization effort of Jedwab and Storeygard (2021) benefited from funding under the DFID/World Bank’s Strategic Research Program on Transport Policies for Sustainable and Inclusive Growth.

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