Geospatial impact evaluations (GIEs) rely on subnationally geo-referenced intervention, outcome, and covariate data and quasi-experimental methods of causal inference to measure the intended (or unintended) impacts of development programs.
GIEs seek to mimic the conditions of a randomized control trial (RCT) with observational data. RCTs are powerful because they create conditions under which one can reliably ascertain that individuals’ participation in a program was not correlated with their outcomes. GIEs create similar conditions, but without randomly assigning individuals to treatment and control groups.
For our in-depth exploration of GIEs, please see A Primer on Geospatial Impact Evaluations Methods, Tools, and Impact Evaluations.
Using counterfactuals to find impact
The key is making comparisons across individuals who are sufficiently similar to one another and experiencing changes that are otherwise similar. The best way to make such comparisons is to identify comparison individuals who are geographically close to the program participants, but unlikely to be affected by the program’s presence. Doing so requires geographically precise data on programmatic interventions and their intended (or unintended) outcomes. Such data are rapidly expanding in number, scope, periodicity, and availability.
Rather than using randomization to identify counterfactual cases, GIEs seek to achieve a similar result through one of three methods:
- Strategic subsampling of observational data to identify treatment and control cases that are nearly identical but for the presence or absence of the intervention (e.g. propensity score matching)
- Comparing the pre- and post-intervention change in the outcome of interest for a treatment group relative to a control group (e.g. difference-in-differences, fixed effects)
- Exploiting the discontinuity around a geographic cutoff that is “as-if random” (where the treated cases and control cases on either side of the cutoff are extremely similar across pretreatment covariates)
Applications and limitations
GIE methods can be applied either retrospectively (for completed projects) or prospectively (for active or future projects). However, they cannot be applied to all types of development programs. The two main constraints to GIEs are the availability of data on the intended outcomes and the spatial distribution of the interventions. While outcome data are rapidly expanding in type and time periods, they are not available retrospectively for all sectors. Secondly, GIEs are feasible for spatially differentiated interventions —those that take place in some locations but not others. A development program that provided, say, budget support or analytical and advisory support to the central government would not likely be evaluable with GIE methods. However, programs that demarcate newly protected areas, construct networks of primary health clinics, strengthen municipal governance systems, or provide agricultural extension support to farmers working on specific plots of land would likely be evaluable with GIE methods.