Estimation Challenge: Ranges, Not Guesses

Objective

Practise estimating with honest ranges and recognise overconfidence in forecasts.

Materials

• A list of ten questions with known answers (for example the length of a river, the population of a city, a figure from your industry)
• Answer sheets
• A pen per team

Step by step

1. Explain the rule: for each question, give a low and high number so that you are 80 percent sure the true answer lies between them.
2. Teams of three to five work through the ten questions in 15 minutes.
3. Reveal the answers one by one; teams count how many fall inside their ranges.
4. A well-calibrated team should get about eight out of ten; discuss whether your ranges were too narrow or too wide, and why.
5. Introduce two techniques: start from a similar known number, and break the question into parts.
6. Run a second set of five questions and compare results.

Facilitator tips

• Make it clear that wide ranges are allowed; the goal is honesty, not precision.
• Link the debrief to real estimates at work: sales forecasts, project durations and budgets.

Variations

• Add yes/no questions with a probability, such as "70 percent likely".
• Play it in the opening session of a planning meeting.

Accessibility

Seated, low-energy activity that works in the room or online. Questions can be shown on screen and read aloud.