This setup can also allow for the evaluation to pick up the effects of differential exposure to treatment: that is, the effect of receiving a programme for more or less time. Studies that do exist have more commonly been applied in the energy and w'ater domains (Ferraro and Hanuauer 2014). Box 2.1 summarises an example of an RCT study applied in the context of biodiversity, to evaluate a forest PES programme19. Vianna and Feamside (2014) use an RCT in Brazil to evaluate the effect of decentralised forest management on number of trees damaged per harvested tree and on carbon stocks.