These look systematically at whether the evidence is consistent with what would be expected if the intervention was producing the impacts, and also whether other factors could provide an alternative explanation. Other methods are also available13 and several guidance documents and handbooks exist. The interested reader can refer to Gertler et al. ( Once impact evaluation results are available, they can be combined with information on programme costs to analyse cost-effectiveness (if possible, a fully-fledged cost-benefit analysis should be carried out (OECD, 2018, Gertler et al., An ex-post CEA addresses the question of how far objectives have been achieved, and at what cost. The cost-effectiveness of a policy is calculated by dividing the annualised costs of the option by a quantified measure of the physical effect, such as animal or plant species recovered, tonnes of emissions of a given pollutant reduced, kilometres of river length restored, and so on (Gorlach, n.d.).