Delphi method

The Delphi method is a structured, iterative technique for soliciting and refining expert opinion, originally developed for forecasting purposes. In health technology assessment (HTA) and economic evaluation, this method has been adapted (sometimes referred to as ‘modified Delphi’) to assess assumptions and estimate parameters (e.g. for economic models) when empirical data are scarce or biased. This method involves experts anonymously responding to questionnaires, receiving summarised group feedback, and then revising their responses over several rounds until consensus is achieved. Key aspects of the process include the selection of appropriate experts, carefully designed questionnaires and iterative feedback. Expert anonymity is also important so that the participating individuals are not influenced by the dynamics of a group discussion. There is no guarantee of reliability (different panels may come to different consensus views); therefore, sensitivity analysis may be required to test the impact of uncertainty in parameters derived by this methods. HTA bodies, such as NICE, generally prefer data from observational studies over expert opinion.