ABSTRACT
For anyone who has ever been in the catacombs of the London Underground it is not hard to remember the characteristic and polite warning issued every time the doors of a train open. At each station thousands of people entering and leaving the trains are dutifully reminded of the small distance between train and platform by the familiar words "Mind the Gap." With some imagination one could think of a situation where people are not minding the gap, possibly resulting in stumbling, getting stuck in or even falling into the gap between train and platform. Nowadays, there is a plethora of policy-oriented research and evaluations of interventions and programs carried out by evaluators but also by auditors and policy analysts. Historically, evaluations have been shaped by the academic disciplines of the evaluators conducting the work. One can distinguish between three types of theory in evaluation: social science theory, evaluation theory and program (or intervention) theory.
