Methodology: your questions about our sauna ratings

Where do the numbers on a sauna card come from?

From the exact Amazon listing that card describes, and from nowhere else. We read the listing title and feature bullets for four things: a stated person capacity, a named panel type, low-EMF wording and a named cabin wood. Each match is stored with the phrase it came from and a note of where it was read, so any figure on this site can be traced back to a line of seller text.

Those four attributes feed a formula. Nothing is inferred from a similar model, a competing listing, a review or a manufacturer website that describes a different configuration. A cabin that states none of the four is not guessed at — it is scored on how completely the listing is documented instead, and the label under its score says which of the two methods produced it.

What exactly are the two formulas?

Documented spec fit = 100 × [0.40 × min(stated person capacity / 4, 1) + 0.25 × spectrum score + 0.20 × (a low-EMF claim appears in the listing ? 1 : 0) + 0.15 × (a cabin wood is named ? 1 : 0)], rounded to a whole number. The spectrum score is 1 for a full-spectrum listing, 0.75 for a far-infrared listing and 0 when the listing names no panel type. Person capacity must be stated in the exact Amazon listing text with the word “person”; the low-EMF term is recorded as a manufacturer claim copied from the listing, never as an emission measurement of ours. This index summarizes how completely a listing documents cabin size, panel type, EMF wording and material — it is not a comfort test, a temperature measurement, a safety judgment and never a statement about any effect on the body.

Documentation completeness = 100 × [0.5 × min(feature bullets / 8, 1) + 0.3 × min(listing images / 5, 1) + 0.2 × (brand stated ? 1 : 0)], rounded to a whole number, computed from the stored Amazon listing record when the listing text never states a person capacity. It measures how completely a seller documents a listing — nothing about how the cabin performs or feels.

The split matters more than either formula. Roughly a third of the cabins in this catalog state a person capacity in their listing text; the rest do not, and pretending otherwise would be the easiest lie available to us.

Why do you trust a listing’s low-EMF claim only as a claim?

Because we have not measured anything. Testing electromagnetic emissions requires a meter, a repeatable protocol, a fixed measurement distance and physical access to each cabin. We have none of those, and a comparison site that publishes emission rankings without them is inventing numbers.

So the low-EMF term in our formula records one fact: the seller addressed the subject in writing. That is worth a fifth of the spec-fit score because a listing that names its EMF position is better documented than one that ignores it — and it is worth nothing more than that. Our low-EMF comparison repeats the same caveat on the page itself.

How do Amazon reviews enter the rating?

Where Amazon publicly displays customer reviews for a listing (average star rating and review count captured from the public product page), the raw editorial score is 100 × [0.45 × (Amazon average / 5) × min(review count / 50, 1) + 0.35 × min(log10(1 + review count) / log10(1 + 5000), 1) + 0.20 × documentation score / 100]. The confidence factor min(review count / 50, 1) damps averages based on very few reviews, and the logarithmic volume term rewards large public review volumes, so widely and highly reviewed listings rank ahead of thinly reviewed ones. Listings with no captured public review data use the documentation score alone. This combined index reflects the public Amazon reputation and the listing documentation — it is not a physical test and not our own product testing.

Two design choices are worth naming. The confidence factor stops a cabin with four five-star reviews from outranking one with two thousand, and the logarithmic volume term keeps the biggest sellers from running away with the list entirely. Where we captured no public review data for a listing, the documentation score stands alone and the card shows no star figure at all.

What does 8.7 out of 10 actually mean here?

Raw documentation scores are normalized across our full catalog to a 5.1–9.9 editorial display scale; ranking order always follows the raw documented score. The displayed value is an editorial index of listing documentation — not a physical test result and not a customer review.

Read it as a documentation index, not a verdict. An 8.7 means this listing documents its cabin more completely, and carries a stronger public review record, than most of the catalog around it. It does not mean the sauna is better built, more comfortable or safer than an 8.1 — those are questions a product page cannot answer and we do not pretend to. Within each comparison, displayed values decrease strictly wherever the underlying raw scores differ, so the visible order always matches the arithmetic.

What never appears on this site?

No claim about any effect of infrared on the body, in any phrasing, anywhere in our own copy. No installation guidance: we report the voltage a listing states and refer every question past a standard household outlet to a licensed electrician. No prices, stock levels or review counts baked into a static page — those render client-side from data inside its validity window, with the collection time shown. No physical test results, because we have run none.

How do I report something wrong?

Write to [email protected] with the page URL, the listing identifier and the statement concerned. Because every extracted attribute stores its source phrase, a correction about a capacity, a wood or a voltage is usually verified in minutes. The affiliate disclosure covers the commercial relationship, and the editorial charter states the principles these formulas implement.