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Why is fibonacci used in wideband Delphi and the Scrum planning poker estimation methods?

The Fibonacci sequence is used in Wideband Delphi and Planning Poker primarily because of its ability to represent relative estimation in a way that accounts for increasing uncertainty as the size of tasks grows. Here are the reasons why the Fibonacci sequence is effective for these agile estimation techniques:

1. Handling Uncertainty and Complexity

  • Natural Growth Pattern: The Fibonacci sequence grows exponentially, which naturally reflects the increasing uncertainty and complexity involved in estimating larger tasks.
  • Diminishing Accuracy: As task size increases, our ability to estimate accurately diminishes. The larger gaps between Fibonacci numbers (e.g., 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144,…,) help express this increasing uncertainty.

2. Encourages Discussion

  • Promotes Conversations: When estimates diverge significantly (e.g., one person estimates a 3 and another a 13), it prompts a discussion. These discussions are crucial for uncovering hidden assumptions, misunderstandings, or risks.

3. Relative Estimation

  • Comparative Assessment: The Fibonacci sequence allows team members to think in terms of relative size rather than absolute effort. This helps in comparing tasks and deciding if one is significantly larger or smaller than another.

4. Simplicity and Usability

  • Intuitive: The Fibonacci sequence is simple and easy to remember. Its use reduces cognitive load, allowing team members to focus on discussion rather than the mechanics of estimation.
  • Limited Choices: Providing a limited set of options helps prevent over-analysis. This “bounded” approach is known as the “satisficing” principle in decision theory, where having fewer choices can lead to better decision-making.

5. Consistency Across Teams

  • Standardisation: Using the Fibonacci sequence helps standardise estimation practices across different teams within an organisation. This consistency is valuable for scaling agile practices.

Application in Wideband Delphi and Planning Poker

Wideband Delphi

  • Expert Estimation: Experts estimate tasks independently using Fibonacci numbers, then discuss differences in a group to reach a consensus. The Fibonacci sequence facilitates the discussion by making significant differences in estimates more apparent and promoting conversation around these differences.

Planning Poker

  • Collaborative Estimation: Team members use Fibonacci cards to estimate user stories during planning sessions. The use of the Fibonacci sequence helps to quickly highlight differences in perception of task size, fostering discussion and ultimately leading to more accurate and agreed-upon estimates.

Estimation is a problem for Enterprise (Domain) Architects as well which is why a method like these could help the Domain Architects in deciding how much time, risk, expertise, effort etc. could be involved in the work they are meant to achieve over a time boxed period.


The Fibonacci sequence’s exponential growth pattern mirrors the increasing uncertainty and complexity associated with estimating larger tasks. Its simplicity, ease of use, and ability to facilitate meaningful discussions make it an excellent tool for agile estimation techniques like Wideband Delphi and Planning Poker.

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