Risk · Plan

Experiment design

Turns the riskiest assumption into the smallest test that could disprove it, with success and failure written down before the experiment runs.

Stage

04 Plan

Works at

Business, Department

Maturity

An idea → Established SME

Time

Two hours to design, then the length of the experiment to run

What it is

Where assumption mapping and the stress test identify what to worry about, this designs the actual test. One assumption at a time, isolated from the others, with the smallest test that would give a genuine answer, and — the discipline almost everybody skips — the success and failure thresholds written down before anyone sees the result.

Isolate one assumption: Not the whole case — the single riskiest assumption, tested on its own. A test that tries to validate three things at once cannot cleanly tell you which one failed.
The smallest test: The cheapest, fastest version of a test that would still produce a genuine answer. A three-month pilot to test something a landing page and a week could answer is expensive caution, not rigour.
Success and failure thresholds, set in advance: Written down before the experiment runs and before anyone has seen data. A threshold set after seeing the result is not a threshold, it is a rationalisation.
The decision rule: What happens on success, and — just as specifically — what happens on failure, agreed by whoever is accountable for the case before the test begins.
Team and approval: Completed with the experiment team before seeking steering group approval, so the design has already been pressure-tested before it is presented.

The mistake people makeSetting the success threshold after seeing early results, which quietly turns a test into a confirmation exercise. The threshold is only meaningful if it is fixed before the data exists.

What it’s forA specific assumption has been identified as the one most likely to break the case, and needs testing rather than continuing to be believed on faith.

What it’s not forThe assumption identified is not actually the riskiest one, or is cheap enough to simply act on and observe rather than formally test. Not every assumption needs an experiment.

How you run it

Isolate the single riskiest assumptionNot the whole case. One assumption, tested cleanly, so the result can be attributed to it specifically.
Design the smallest test that gives a real answerThe cheapest, fastest version that would still be genuinely informative — resist the pull toward an expensive test that feels more rigorous than it needs to be.
Write the success and failure thresholds before running itFixed before anyone has seen a result. A threshold set afterward is a rationalisation, not a test.
Agree the decision rule for both outcomesWhat specifically happens on success and on failure, agreed by whoever is accountable for the case, before the experiment begins.
Run it with the team, then take it to the steering groupPressure-tested with the people closest to the work before it is presented for approval — not designed and approved in the same room for the first time.

The prompt

Two ways to run it

Run this tool in your own Claude

The short prompt starts your partner against the library on your disk. The long one carries everything with it and needs nothing installed.

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🔒 Prompt locked

Everything above is free — what this tool is, what it is for, what it is not for, and how to run it as a workshop. Three tool prompts a month are free with an account; beyond three, and for the printable canvas, it is the paid part.

See plans — from £19 a month

Your playbook

It lands in the earliest stage this tool suits. Move it on the Playbook page.

You’ll need

The specific assumption being tested, isolated from every other assumption in the case
What would count as success and what would count as failure, before the experiment starts
The smallest, cheapest version of the test that would still give a real answer

You’ll end up with

A single, isolated assumption with a specific test designed for it
Success and failure thresholds written down before the result is known
A decision rule for what happens on each outcome, agreed in advance

Runs well with

AI operating model options AI risk classification and governance Alliance and partnership design Assumption log