Theory based evaluation is interim measure of implementation

EDITOR—As I produced the first description of theory based evaluation,1 readers might imagine that I would welcome Prideaux's support for the approach.2 Alas, no.

The point of theory based evaluation is to see, firstly, to what extent the theory is being implemented and, secondly, if the predicted outcomes then follow. It is particularly useful as an interim measure of implementation when the outcomes cannot be measured until much later.

But most (if not all) theories in social science are only sets of persuasively stated hypotheses that provide a temporary source of guidance. In order to see if the hypotheses can become theories one must measure the extent to which the predicted outcomes are achieved. This requires randomised controlled trials. Even then the important point is to establish the direction and magnitude of the causal relation, not the theory. Many theories can often fit the same data.

To suggest that controlled trials would be unethical because some postgraduates “would be given no choice over the learning methods they will engage in” is to raise issues that surround the conduct of any clinical trial. It …