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Method 08 · Condense and decide

Delphi Survey

The Delphi method surveys a group of experts in several rounds, in writing and anonymously; after each round everyone receives the condensed group view and may revise their estimate. Anonymity takes status and rhetoric out of play, the feedback lets outliers state their reasons — and often it is precisely the dissenters' reasoning that is most valuable. Delphi delivers no truth, but a robust, traceable condensation of what informed people consider probable, together with the places where they remain divided.

ROUND 1ROUND 2ROUND 3 Dissenter with reasons Distribution → uncertainty band of the roadmap earlierlater
Three rounds: the spread narrows, one dissenter remains — and their reasoning is often the most important finding. The final distribution becomes the uncertainty band.

Procedure

  1. Formulate the questions. Precisely, quantifiably where possible: "When will technology X reach TRL 8?" instead of "How do you see the future of X?"
  2. Assemble the panel. Diversity over size: different disciplines, industries, standpoints. Ten to thirty people usually suffice.
  3. Round 1. Anonymous, in writing; estimate plus brief reasoning.
  4. Feedback. Distribution of answers and the reasons of the dissenters, to everyone.
  5. Round 2 (and possibly 3). Revision permitted; stop when the distribution stabilises — not only at consensus.

Strengths

  • Removes hierarchy and volume from the formation of judgement.
  • Shows not only the median but the spread — and thus the real uncertainty.
  • The dissenters' reasons are often the actual insight.

Limits

  • Costly and slow; response rates fall over the rounds.
  • Experts err collectively — Delphi does not average errors away.
  • Quality stands and falls with the wording of the questions.

How we use it in our roadmaps

We use Delphi selectively where scanning and bibliometrics yield no timeline — for breakthroughs whose timing only specialists can estimate: error-corrected quantum computers, commercial fusion, humanoid robots in routine operation. The Delphi results enter the roadmap timeline as milestones with spread; the spread becomes the uncertainty band.

In the source apparatus we document which assessment stems from a Delphi round, how large the panel was and how wide the distribution. A Delphi milestone with a tight distribution is a different statement from one where the experts disagree by ten years — both are valuable, but different.

References