A five-star average from one review and a three-star average from nine reviews do not combine into four stars. Before a website supplier publishes an aggregate, establish the underlying counts, scale and eligible records. Correct arithmetic is separate from permission to display reviews or eligibility for search-result stars.
Who should use this acceptance brief
Businesses commissioning review summaries and trust sections. Use this as a scoped website handover task. Where real system evidence is required, teaching examples are not a substitute.
Source-bound platform fact
Google’s review guidance requires accurate supported review information and restricts self-serving LocalBusiness/Organization review snippets. Valid numbers alone do not establish rich-result eligibility. Google: review snippets · Checked 16 October 2026.
Filled teaching example
Synthetic example, not a client case. Finite inputs, expected decisions and counterexamples follow; no live integration is claimed.
On narrow screens, scroll to read the complete table.
| Input / case | Check basis | Expected decision |
|---|---|---|
| 1×5 +9×3 | 10 reviews | 3.2 weighted |
| simple (5+3)/2 | ignores counts | 4.0 is wrong for this set |
| group missing count | insufficient input | unknown |
Run the acceptance exercise
- Obtain permitted source counts, rating scale and inclusion rules without publishing private reviewer data.
- Recompute from raw eligible ratings where available, otherwise explicitly bounded aggregates.
- Review display permission, visible evidence and schema eligibility separately.
Interpret the result and retain evidence
The fixture uses synthetic groups and computes a count-weighted arithmetic mean. It cannot verify authenticity or whether groups overlap. Do not merge repeated reviews from two exports as distinct people. The page contains Article markup only; the teaching figures are never published as MadRaven’s own customer rating.
Limits before implementation
No real customer reviews, testimonials or aggregate-rating schema are created. No promise of search stars or conversion improvement.
Replay the finite example
Save both files in one folder and run with Node22.13 or newer. The example sends no network requests and changes no account or site. Filled inputs and expected outputs · Inspectable functions
node decision-check.mjs review-average-evidence-contract.json