Turn the observation into a hypothesis
Start with a concrete friction point and the evidence supporting it. A session recording can suggest a problem to investigate; it does not by itself establish how common the problem is. Combine the observation with suitable journey data and product context before choosing a variation.
Write the proposed mechanism in plain language. For example: placing accurate size guidance beside the selector may help eligible mobile shoppers choose confidently. Name the affected audience and the outcome you expect to change. Keep unrelated design changes outside this variation so that the result remains interpretable.
Set outcomes and guardrails before launch
Microsoft’s experimentation guidance separates overall outcomes, diagnostic measures, guardrails and data-quality checks. Its pre-experiment and during-experiment guidance also highlights trustworthy assignment and the risk of misreading early results. These principles help structure the plan; they do not supply one universal sample size or duration for every store.
For a fashion test, discuss completed purchases as an outcome, use of size guidance as a diagnostic and returns as a later commercial check. Agree how you will inspect page speed and assignment quality. Specify an analysis method, sample requirement and stopping rule with the experiment owner before launch.
Source: Microsoft Research: pre-experiment checks ↗ · Microsoft Research: reviewing running experiments ↗
Validate the experience people will actually receive
Check the control and variation on common mobile widths, including long product titles and unavailable sizes. Verify the actual allocation, exposure and purchase events. Confirm that a returning visitor does not unexpectedly switch variants and that overlapping experiments are understood.
Prepare a rollback owner and an operational failure rule. Stopping a broken experience to protect users differs from declaring a statistical winner because an early chart looks promising. Preserve the reason for any intervention so the final report can explain what changed during the test.
Make the result include uncertainty and follow-through
Report the sample, estimated effect, uncertainty, guardrails and whether the agreed decision conditions were met. A running experiment remains a running experiment. If the result is inconclusive, explain which useful question remains instead of converting the most attractive number into a success claim.
Attach the proposed next action: adopt, iterate, stop or collect the evidence required by the original plan. Record later return outcomes where they matter. The CRO Agent can help prepare the investigation and proposal; the responsible team reviews the method and authorises implementation.
A size-guide experiment brief
Illustrative brief: eligible mobile product-page visitors are assigned to the existing size selector or a variation with a clearer guidance link. The team checks exposure and allocation, predefines the primary outcome and stopping method, and watches performance regressions. A rise in guide clicks alone is not the win condition. Later purchase and return evidence informs the commercial review.
Turn the guide into a useful review
- Document evidence, mechanism and eligible audience.
- Agree primary outcome, guardrails and analysis method.
- QA both variants, assignment and event collection.
- Report uncertainty and apply the agreed decision rule.
Reference material
Platform guidance checked 3 October 2026. Examples and working checklists are Faccelerate editorial illustrations.
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