Since the 1970s a great number of community-based or population-based intervention studies have been carried out, for prevention of cardiovascular diseases, but also for prevention of other related chronic diseases.1-3 The basic idea is that the intervention is targeted to the total population living in the community or in a defined area.

The principles and methods of evaluation have been developed and discussed along with those projects.4-6 Commonly the evaluation is concerned with the outcome. Here different levels of objectives have been used: mortality, incidence, risk factors, health behaviours, etc. At the same time it is most useful to understand how and why the programme has worked, so that possible success can be replicated. This process evaluation is concerned with assessing changes in the intervening variables and calls for a theoretical framework of the intervention.

The evaluation study design is another issue. A true experimental design would have a number of communities to be allocated randomly into intervention and control communities. This is seldom possible and one might also ask how much …