The central element of theory-based evaluation approaches involves developing the theory for why the program should achieve its desired outcomes. It is this stage that distinguishes theory-based evaluations from other approaches. Chen ( 1990) differentiates between two models for developing program theory: (a) the stakeholder approach, in which the evaluator works with stakeholders, typically key program people, to discover their reasoning or underlying assumptions for program success; and (b) the social science approach, in which evaluators make use of their own knowledge both of the program and of the social science theory and research to develop a model.