Research in the field of pharmacoeconomics has increased substantially during the past decade. Much of this research has been on the design and analysis of data concerning the relative merits of one drug or device compared with another in terms of costs and effects. Concomitant with these evaluations has been the development of guidelines for the conduct of economic evaluations in several countries. However, despite an increase in research, little attention has been paid to how different study designs may influence the results of a study. The use of expert judgement in decision analytic modelling is one area where design issues may influence the findings of a study. This issue is examined for the case of modified Delphi and Delphi panels. Although the use of expert opinion in modelling studies seems to be widespread, there is little consistent application, understanding or reporting of the techniques used. In particular, the definitions of techniques vary between studies, the criteria for determining when consensus is reached vary, and the reporting of these criteria is absent. Future studies using expert judgement should be more aware of the controversies surrounding the issue and provide more reporting of the techniques used. It is proposed that future validation exercises may assist researchers in determining the most appropriate application of methods.