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Figure 2From “What is reference class forecasting?”

A reference class forecast record

Write down the plan figure, the class, its distribution and the case's position before the adjusted number goes into a budget.

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Figure 2A reference class forecast record

A six-column worksheet for a reference class forecast: the decision the number informs, the inside view estimate and how it was built, the reference class and how its cases were chosen, the class distribution as actual over plan at stated percentiles, the evidence that this case differs from the class, and the forecast at the certainty the decision needs.DecisionWhat will thisnumber decide?Inside viewPlan figure,built how?ClassWhich pastcases, chosenhow?DistributionActual overplan, whichpercentiles?PositionEvidence thiscase differs?ForecastNumber at thecertaintyneeded?Read the percentile the decision needs. Shift the case only on evidence that this team plans better, orworse, than the class did.

Source: Author's decision worksheet. The inside view field follows Kahneman and Lovallo (1993), p. 25; the class and distribution fields follow Flyvbjerg (2008), p. 8, and Kahneman and Lovallo (1993), p. 25; the position field follows Flyvbjerg (2008), p. 16; the forecast field follows Flyvbjerg (2008), pp. 12 to 16; the warning on classes recalled from memory follows Lovallo et al. (2012), pp. 500 and 509. The decision field and the application to revenue are this guide's own. The fields are reader inputs; no company data is supplied.

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Each line names a claim related to this exhibit, its source, and how it was checked.

  • B RCF-OWN-C3 A reference class forecast is written down as one record: the decision, the inside view figure and how it was built, the class with its sources and inclusion rule, the distribution in a size-free unit such as actual over plan, the evidence for placing the case above or below the class middle, and the forecast at the certainty the decision needs; two separate questions: the certainty the decision needs sets which percentile is read, and the position field shifts the case within the class only on evidence and in either direction, after Flyvbjerg's rule on lower and higher uplifts (revised after G5 F1, which found the worksheet footer one-sided and in conflict with the illustration); illustrated with a hypothetical add-on whose first-year bookings plan is set against the ratio of actual to plan in the firm's own and, where available, other firms' launches, using a low percentile for a revenue figure (a shortfall risk) and the median for a portfolio, a shift toward the plan figure if the team's past launches came closer to their plans than those in the class and further below it if they fell further short, a note when the class is small or recalled from memory (which may come out small and favourable, as in Lovallo et al.'s questionnaire), and both figures kept for a later comparison with the actual. Untested.Author worksheet grounded in FLY08-C3, FLY08-C4, KL93-C1, KL93-C6 and LCC12-C2

Grades: A, verified against the printed page of the primary source · B, primary source, text layer only · C, authoritative secondary · D, reported.

From the essay

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APA 7

Isoglu, S. (2026). A reference class forecast record [Figure]. isoglu.com. https://isoglu.com/insights/exhibits/isoglu-2026-what-is-reference-class-forecasting-fig02/

BibTeX
@misc{isoglu-2026-what-is-reference-class-forecasting-fig02,
  author = {Isoglu, Sinan},
  title = {{A reference class forecast record}},
  year = {2026},
  howpublished = {Figure 2, isoglu.com},
  url = {https://isoglu.com/insights/exhibits/isoglu-2026-what-is-reference-class-forecasting-fig02/},
  note = {From the essay {What is reference class forecasting?}}
}
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<figure>
  <a href="https://isoglu.com/insights/exhibits/isoglu-2026-what-is-reference-class-forecasting-fig02/">
    <img src="https://isoglu.com/social/isoglu-2026-what-is-reference-class-forecasting-fig02.png" alt="Figure 2: A reference class forecast record" width="3200" height="2400">
  </a>
  <figcaption>Figure 2: A reference class forecast record. Source: Author&#39;s decision worksheet. The inside view field follows Kahneman and Lovallo (1993), p. 25; the class and distribution fields follow Flyvbjerg (2008), p. 8, and Kahneman and Lovallo (1993), p. 25; the position field follows Flyvbjerg (2008), p. 16; the forecast field follows Flyvbjerg (2008), pp. 12 to 16; the warning on classes recalled from memory follows Lovallo et al. (2012), pp. 500 and 509. The decision field and the application to revenue are this guide&#39;s own. The fields are reader inputs; no company data is supplied. <a href="https://isoglu.com/insights/exhibits/isoglu-2026-what-is-reference-class-forecasting-fig02/">View exhibit</a>.</figcaption>
</figure>

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