Minimal Number of Experts in Delphi

Maximum 30 Experts in Delphi
Ipshita Guha, Partner, India
The maximum number of Delphi experts should not be more than 30.
Too many experts will dilute your process, too few will not yield the required diversity that is required for you to learn and gather inputs.

Minimum and Maximum Number of Participants in Delphi Method
H D SHARMA, Professor, India
I don't think there can be any such limit of maximum number. I have conducted Delphi studies reported in Technological Forecasting and Social Change (44,2,1993) in which some 93 participants helped in consensus.
In fact Mr. Gharaibeh asked for minimum number and not maximum. Theoretically there is no lower bound on the number but the number should be large enough so as to reach a realistic consensus.
It should be kept in mind that Delphi is a consensus methodology and the arrived consensus should not seem to be contrived. Inter round drop off of around 10 to 15 % is to be expected in most cases.