This paper compares two families of evaluation techniques for social programmes in the field of employment and income. The first refers to the experimental methods and in particular to the randomised control trials, which are of increasing use in the evaluation of social programmes. The second refers to the structural economic modelling of individual behaviours supposed to be important determinants of the policy being evaluated. Although the emphasis of the paper is more on experimental methods, because of their relative novelty in the economic discipline, it essentially argues that no method should be preferred to the other on a priori grounds. They both have advantages and limitations in their applicability. Ideally they should be used concomitantly as they have some power to partially compensate the deficiencies of each other.