Delphi Method

When to use it
Use it to explore an issue with a distributed group of people.
Use it to move a group of people towards consensus.

How to use it
Define the problem
Identify the problem that you want to work on, writing it down in a clear way that is easy to understand. This can be in various forms, from a questionnaire to a broad and open question.
You can work on one problem and you can work on several problems at once. The constraint is usually the bandwidth and expertize of the people in the Delphi group.
Give everyone the problem
Recruit people to the Delphi group. This includes anyone who has been selected to contribute thinking on this project. There is seldom a meeting needed for Delphi work, making it ideal for virtual teams.
Delphi thinking can be done with a small group and it can be done with hundreds of people. Around 20 people is a fairly common size.
Send the problem or problems to everyone who is in the group and ask them respond. You will have to handle a lot of feedback, so asking for short bullet-points will make things much easier to deal with than rambling text.
Collate the responses
Take the responses that people send back to you and collate these into a single anonymous list or sets of lists.
Make this as easy as possible for the people to read when you send it back out again, but be aware of causing inappropriate bias. For example you may group responses into appropriate headings, but with the caution that this might presuppose particular thinking.
On the other hand, if you are seeking creative ideas you may deliberately mix up the answers.
Give everyone the collation
Send the collation back out to everyone with the request to score each item on a given scale (typically 1 to 5). You may also allow them to add further items as appropriate.
Remember to include the original problem at the top of the page, along with instructions on what to do. You can also make responding easier by putting the items in a table with space for the score.
Repeat as necessary
The process may now be repeated as many times as is deemed appropriate. If you are seeking consensus and there was a wide range of responses, then this may require several iterations. In particular at least a second round to see how others have scored can be very useful.
In analysing the scores, one method used in Delphi analysis for smaller groups and especially when percentage scores are used is to use the formula: (lowest score + highest score + 4 x average score) / 6. This gives more weight to the average whilst also allowing some influence from outliers.
Example
Given a problem around valve leakage, a community of engineers decide to use a Delphi group to explore ideas. A part of the table they come up looks like this. This could be done in a simpler table, but hey, this is engineers!