Coaching practices for Fermi Estimation During a Big Change

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Does this sound like the set of challenges you might be facing?

  • My guesses never seem to get any better because I make them, find out the real answer, and then just move on
  • I land on a number and just go with it, never pausing to ask what’s the most it could possibly be or the least
  • My answer came out wildly off and I can feel that it’s wrong but can’t spot where
  • I tend to blurt out one confident-sounding number and act like it’s solid, when honestly I have no business being that sure
  • The question is so big and tangled that I just go with my gut and blurt out a number, and it feels like a guess because it is one

Practices that may help

  1. Track your estimates and calibrate
    Compare your Fermi estimates to actual figures when you can, and use the gap to improve future estimates.
    Fermi Estimation
  2. Fermi Estimation
    Fermi estimation is the practice of making rough but principled quantitative estimates by decomposing an unknown into knowable sub-problems, estimating each, and combining them. Named for physicist Enrico Fermi, who was renowned for accurate estimates from minimal data, it is used in science, engineering, and everyday decisions to calibrate intuitions and check whether a number is in the right ballpark — not to achieve false precision.
  3. Sanity-check against known extremes
    Test your estimate against the clearly too-high and too-low bounds to calibrate your range.
    Fermi Estimation
  4. Check units and scales for consistency
    Catch order-of-magnitude errors by ensuring your units are consistent across the estimate.
    Fermi Estimation
  5. Estimate in ranges, not point estimates
    Instead of "my estimate is 500," say "I think it is between 200 and 2000."
    Fermi Estimation
  6. Decompose complex questions into sub-questions
    Break a hard forecasting question into smaller, estimable pieces and aggregate them.
    Superforecasting
  7. Anchor on what you know and scale from there
    Start from a number you are confident about, then reason to the unknown.
    Fermi Estimation
  8. Update beliefs frequently and in small increments
    When new evidence arrives, adjust your probability estimate — even if the change is small.
    Superforecasting
  9. Update your forecast incrementally as new evidence arrives
    Treat your forecast as a probability that should shift with each new piece of evidence, not a commitment that survives contradiction.
    Reference Class Forecasting
  10. Update beliefs incrementally, not all at once
    New evidence should shift your probability somewhat — rarely from 5% to 95% in one step.
    Bayesian Thinking: How to Update Beliefs Rationally

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