The ecological or social ecological model looks upon an institution as a system or organisation embedded within a specific context. Kurt Lewin (1935) maintained that events could not be considered in isolation from their context. Behaviour is a function of person-environment interactions. Explanations of the functioning of a system or organisation are concerned with the functions of the system as a whole and its subsystems. Systems are envisaged as multi-level and multi-factorial, that is there are different levels of analysis and different factors to be considered when describing any given system. Institutions are perceived as having a number of functions that can be evaluated.