5Brett A. Bryan ,John M. Kandulu. Designing a Policy Mix and Sequence for Mitigating Agricultural Non-Point Source Pollution in a Water Supply Catchment, Water Resource Manage,2011, Vol. 25:875 - 892.
6Paul R. Rosenbaum, Donald B. Rubin. The Central Role of the Propensity Score in Observational Studies for Causal Effects, Biometrika, 1983 ,Vol. 70:41 -55.
7Brent M. Simpson, Michelle Owens. Farmer Field Schools and the Future of Agricultural Extension in Africa, Journal of International Ag- ricultural and Extension Education ,2002, Vol. 2:29 - 36.
8Erin M. Godtland, Elisabeth Sadoulet, Alain de Janvry et al. The Impact of Farmer Field Schools on Knowledge and Productivity : A Study of Potato Farmers in the Peruvian Andes, Economic development and cultural change,2004, Vol. 53 ( 1 ) :63 - 92.
9Andrea Pufahl, Christoph R. Weiss. Evaluating the effects of farm programmes : results from propensity score matching, European Review of Agricultural Economics,2009 ,Vol. 36:79 - 101.
10Mariano Mezzatesta, David A. Newburn, Richard T. Woodward. Additionality and the Apoption of Farm Conservation Practices, Land Use, forth coming,2012.