They examine programme implementation in a geographically limited area where territories have relatively similar historical trends, land use patterns, and potentially similar access to information and to infrastructure. Using data on land cover in 2007 and 2013, they estimate that the additional conservation represents between 12 and 14.7 percent of forest area enrolled in the programme in comparison to control areas. It can help evaluate programmes with imperfect compliance, voluntary enrolment, or universal coverage (Gertler et al.