mary posterior” distribution from the summary prior distribution and summary likelihood; (8) choosing a utility function to incorporate costs and stakeholders’ sensitivity to such costs; and (9) decisions based on regrets or opportunity costs in cost–benefit or risk–benefit models by weighing outcome information from summary posterior distribution (e.g., mean differences, risk differences, risk ratios, odds ratios, and interactions involving these effects) against utility functions. Each of these steps is described in more detail below.
Steps 1–2. Selection of a sample of stakeholders and elicitation of probability information from these stakeholders: The selection process should at least be comprehensive, maximizing the number of contrasting points of view, if the process is not random. Stakeholders’ prior opinions will be elicited with questionnaires. In these questionnaires, stakeholders will be asked to provide ranges of probabilities of confidence in positive and negative results. The design of the questionnaire will be selected from several different designs available in the research literature. Chaloner and Rhame (2001) presented an interactive approach based on iterative elicitation from physicians enhanced by real-time iterative and graphical feedback to the physicians of their quantified opinions. Parmar et al. (1994, 2001) and Spiegelhalter et al. (1994) presented a questionnaire for eliciting prior distributions in a pair of large randomized trials conducted as part of the British Medical Research Council Cancer Trials. In a hepatocellular carcinoma clinical trial, Tan et al. (2003) also used such a questionnaire to elicit prior information on the equivalence between surgery with adjuvant therapy versus surgery alone on recurrence-free survival. Alternatively, a series of individual description formats have been developed by Vennix et al. (1994). These individual questionnaire formats focus on the different phases proposed by for elicitation: (1) the positioning phase, which defines the context of the information; (2) the description phase, which guides stakeholders through four aspects of description (visual, verbal, textual, and graphic); and (3) the discussion phase, in which the individual descriptions from phase 2 are examined and compared.
Step 3. Translation of this information to prior distributions: Individual histograms representing the prior beliefs of each investigator can be constructed from the relative probability values that stakeholders may be asked to provide in Step 2. Following Spiegelhalter et al. (1994), these probability values may be summarized across stakeholders with similar opinions to then construct “overall histograms”and “skeptical histograms.”