Testing the validity of cost-effectiveness models

A growing body of recent work has identified several problems with economic evaluations undertaken alongside controlled trials that can have potential ly serious impacts on the ability of decision makers to draw valid conclusi ons. At the same time, the use of cost-effectiveness models has been drawn into question, due to the alleged arbitrary nature of their construction. T his has led researchers to try and identify ways of improving the quality o f cost-effectiveness models through identifying 'best practice', producing guidelines for peer review and identifying tests of validity. This paper investigates the issue of testing the validity of cost-effective ness models or, perhaps more appropriately, whether it is possible to objec tively measure the quality of a cost-effectiveness model. A review of the l iterature shows that there is much confusion over the different aspects of modelling that should be assessed in respect to model quality, and how this should be done. We develop a framework for assessing model quality in terms of: (i) the str ucture of the model; (ii) the inputs of the model; (iii) the results of the model; and (iv) the value of the model to the decision maker. Quality asse ssment is investigated within this framework, and it is argued that it is d oubtful that a set of objective tests of validity will ever be produced, or indeed that such an approach would be desirable. The lack of any clearly d efinable and objective tests of validity means that the other parts of the evaluation process need to be given greater emphasis. Quality assurance for ms a small part of a broader process and is best implemented in the form of good practice guidelines. A set of key guidelines are presented.