The Delphi technique is an iterative process for gaining consensus on an issue from a group of subject matter experts. It has been used very effectively by large organisations for strategic business planning.
The basic process begins with a definition of a problem. In P3 management this could range from the need to prioritise projects and programmes in a portfolio to estimating the duration of innovative activities in a network diagram.
Once the nature of the problem is understood, a panel of experts is identified. Each is sent a questionnaire relating to identifying solutions to the problem.
The panel is not normally brought physically together. This avoids issues of personality and group interaction affecting the responses.
The responses are analysed and if there is consensus the conclusions are summarised. If the first round does not produce consensus then a second questionnaire is prepared that incorporates information from the first set of results.
As the panel considers the results of the first round they tend to gravitate towards a consensus position. This cycle is repeated until consensus is reached or no further convergence is achieved.