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The Delphi Technique is a multistep method used to estimate future demand for a product or service whereby a special group of experts in Risk/Cost/Schedule forecasting exchange views and then each individually submits estimates and assumptions to an analyst who reviews all the data received and issues a summary report. The summary report is then discussed and reviewed individually by the group members who each submit revised forecasts to the analyst, who then reviews the material again and issues a secondary report. This process continues until all participants reach a common ground. The Delphi technique is beneficial when other methods are not adequate or appropriate for data collection. The technique is commonly used in Risk Management.
In 1975 Linstone and Turoff stated that one or more of the following leads one to use the Delphi Technique: 
- The problem does not lend itself to precise analytical techniques but can benefit from subjective judgments on a collective basis.
- The individuals needed to contribute to the examination of a broad or complex problem have no history of adequate communication and may represent diverse backgrounds with respect to experience or expertise.
- More individuals are needed than can effectively interact in a face-to-face exchange. Time and cost make frequent group meetings unfeasible.
- A supplemental group communication process can increase the efficiency of face-to-face meetings.
Also in 1975 Scheele illustrated a process where the opinions and judgments of people familiar with or associated with a subject and they listed a typical sequence of events in the Delphi process in six steps: 
- Identify the group members whose consensus opinions are sought. If the study goes beyond an intact group such that representatives must be selected, care must be taken to insure that all the various publics or positions are proportionately sampled.
- Questionnaire One. Have each member generate a list of goals, concerns, or issues toward which consensus opinions are desired. Edit the results to a manageable summary of items presented in random order. Prepare the second questionnaire in an appropriate format for rating or ranking (Note: If an established or acceptable listing of such items already exists, this first step can be bypassed.).
- Questionnaire Two. Have each member rate or rank the resulting items.
- Questionnaire Three. Present the results of Questionnaire Two in the form of Questionnaire Three, showing the preliminary level of group consensus to each item. Where the individual differs substantially from the group, and chooses to remain so on Questionnaire Three, the respondent should provide a brief reason or explanation.
- Questionnaire Four. The results of Questionnaire Three are presented in the form of Questionnaire Four, showing the new level of group consensus for each item and repeating the member’s latest rating or ranking, along with a listing by item of the major reasons members had for dissent from the prevailing group position. Each member rates or ranks each item for the third and final time, in light of the emerging pattern of group consensus and the reasons for dissent.
- The results of Questionnaire Four are tabulated and presented as the final statement of group consensus.
Program Management risk factors for using the Delphi Technique include:
- Judgments are those of a select group of people and may not be representative;
- Tendency to eliminate extreme positions and force a middle-of-the-road consensus;
- More time consuming than the nominal group process;
- Should not be viewed as a total solution;
- Requires skill in written communication;
- Requires adequate time and participant commitment (about 30 to 45 days to complete the entire process).
AcqLinks and References:
-  DAU Delphi Technique Overview
-  Linstone & M. Turoff (Eds.), The Delphi method: Techniques and applications (pp. 17-35). Reading MA: Addison-Wesley Publishing Co.
-  Scheele. (1975). Consumerism comes to Delphi. Technological Forecasting and Social Change, 7, 215-219.