Agile planning : Wide band Delphi

Wide band Delphi definition

• Wide band Delphi is a group estimation technique.
  • The Wideband Delphi estimation method is a consensus-based technique for estimating effort.

Wide band Delphi hystory

• It derives from the Delphi method which was developed in the 1950-1960s at the RAND Corporation as a forecasting tool.
  • It has since been adapted across many industries to estimate many kinds of tasks, ranging from statistical data collection results to sales and marketing forecasts.
• Barry Boehm and John A. Farquhar originated the Wideband variant of the Delphi method in the 1970s.
  • They called it « wideband » because, compared to the existing delphi method, the new method involved greater interaction and more communication between those participating.
  • The method was popularized by Boehm’s book Software Engineering Economics (1981).

Wide band Delphi practice

• Original steps
  • Coordinator presents each expert with a specification and an estimation form.
  • Coordinator calls a group meeting in which the experts discuss estimation issues with the coordinator and each other.
  • Experts fill out forms anonymously.
  • Coordinator prepares and distributes a summary of the estimates.
  • Coordinator calls a group meeting, specifically focusing on having the experts discuss points where their estimates vary widely.
  • Experts fill out forms, again anonymously, and steps 4 to 6 are iterated for as many rounds as appropriate.
• Where is it effective ?
  • For making top-down estimates in situations where there are a lot of unknowns or various kinds of domain knowledge required.
  • Especially useful for early estimates of large, not-yet-well-understood projects — estimates upon which we base our go/no-go decisions and early expectation-setting for upper management and customers.
• How does it work?
  • step 1 :
    • Schedule the estimation meeting for a particular project or set of projects.
    • The estimators should be team members (and possibly other stakeholders) who are very knowledgeable about the project, and from whom you need buy-in for the schedule of the project.
    • 3-5 estimators is the sweet spot, although much larger groups can work, by breaking them into 3-5 person sub-groups and then combining those estimates.
  • step 2 :
    • Describe what the group is estimating.
    • What part of the project, goals, or outcome are we estimating ?
    • What types of resources are we going to include ?
    • What units (ideal man-days or man-months, story points, etc.) will we use?
  • step 3 :
    • Ask everyone to estimate individually and privately using their best, instinctual judgement on the estimate.
    • Give them enough time (5-20 minutes) to do this work quietly.
    • Once people are familiar, you may be able to ask them to do this before the estimation meeting.
    • Ask them also to take note of the assumptions and major pieces of work that led to the estimate — they’ll use these later in the group discussion.
    • The private/anonymous aspect of this first round of estimates is important: we’re specifically empowering each person to express their gut instinct, and not be influenced by group think yet.
  • step 4 :
    • Show the results on a spreadsheet or whiteboard, and discuss.
    • The group can see how divergent or convergent their estimates are.
    • Ask each person (but especially the high/low or other interesting estimators) to explain how they got to their estimate — major assumptions, things included, etc.
    • People will be reminded of things they forgot to include in their estimates.
    • They’ll also be forced to confront different assumptions (which you may be able to quickly decide upon).
    • All of which will improve future rounds of estimates.
  • Repeat steps 3 & 4 for a total of 2-3 rounds.
• Number of rounds
  • After round one, anonymity is dropped and discussions can be short (the moderator should make decisions on behalf of group, for expediency and just for the purposes of the estimate).
  • Often only 2 rounds total are needed to see estimates converge somewhat.
  • A common effect is estimates converge together and up as people realize from the discussions the things they missed from their initial estimates.

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