Nighttime lights as a proxy for human development at the local level

Abstract

Nighttime lights, calculated from weather satellite recordings, are increasingly used by social scientists as a proxy for economic activity or economic development in subnational regions of developing countries where disaggregated data from statistical offices are not available. However, so far, our understanding of what nighttime lights capture in these countries is limited. We use geo-referenced Demographic and Health Surveys (DHS) from 29 African countries to construct indicators of household wealth, education and health for DHS cluster locations as well as for grid cells of roughly 50 × 50 km. We show that nighttime lights are positively associated with these location-specific indicators of human development, and that the variation in nighttime lights can explain a substantial share in the variation in these indicators. We conclude that nighttime lights are a good proxy for human development at the local level.

Fig 1. Illustration of DHS clusters, nighttime lights and our spatial units for Western Kenya.

Dots represent reported DHS cluster center points from Kenya DHS 2008. Circular zones around these center points (in red) have a 2 km radius for urban clusters and a 5 km radius for rural clusters. The grid cells of 0.5 × 0.5 decimal degrees (in green) are aligned to the PRIO-GRID. Nighttime lights underlay the map, with brighter tones of grey implying more intense nighttime lights.

Fig 2. Distribution of development indicators over bins of nighttime lights.

Graphs show box plots for four development indicators over 11 bins of nighttime light values. The development indicators are: primary school attendance, years of schooling, share of births assisted by professional health personnel, and infant mortality. Spatial units are circular zones of 2 km (5 km) radius around urban (rural) DHS clusters in the left column and PRIO-GRID cells in the right column. In each graph, the first bin contains all spatial units with zero average nighttime light; the remaining bins are based on the deciles of the nighttime lights distribution of the spatial units with above-zero nighttime lights. Boxes indicate the range from the 25th to the 75th percentile (interquartile range), with the median as a horizontal line; whiskers indicate the range of values within up to 1.5 times the interquartile range; and dots indicate values outside this range.

Fig 3. Nighttime lights and household wealth for different country characteristics and over time.

Graphs show the marginal effect of ln(light+0.01) on household wealth for different values of four different modifying variables: GDP per capita (in logs), share of agricultural value added in GDP, Polity2 score, and time (measured in years since 1992). Units of observation are circular zones of 2 km (5 km) radius around urban (rural) DHS clusters in the left column and PRIO-GRID cells in the right column. In each graph, the bold curve shows the point estimate of the marginal effect and the dashed curves the corresponding 95% confidence interval (see Eqs 2 and 3). The grey bars indicate the distribution of the modifying variable.