Stepped wedge cluster randomised trials allow for controlling for variations in timing due to random and sequential crossover of clusters from control to intervention. A 3ie supported impact evaluation in Sudan assesses the impact on incidence and prevalence of moderate acute malnutrition (MAM) in children under five years and pregnant and lactating women of different MAM treatment and prevention interventions. The evaluation design uses variation in the timing of introduction of MAM prevention components (such as food-based prevention, behaviour change communication) and home fortification to localities (clusters) where treatment activities were underway. The impacts are assessed by undertaking a cross sectional comparison across clusters, as well as a comparison over time within the same cluster. This is a good example of a methodology that can be employed for robust causal analysis when baseline data are not available, and where withholding the programme from any group of potential beneficiaries is neither desirable nor feasible.

Ethical considerations

It is sometimes critically viewed that impact evaluation designs require that only some individuals receive the intervention and this brings up ethical concerns.