How we rate evidence.
Every guide and brief on Restadian carries one of four evidence ratings. This page explains what those ratings mean, how we arrive at one, and what would make us change it. If a rating on a page looks wrong to you, this is the document to argue with.
Four levels, defined before the page is written.
The rating describes the state of the research on a question, not our enthusiasm for the answer. A well-evidenced boring finding rates higher than an exciting thin one.
Strong
A well-described mechanism supported by repeated findings across independent groups, with results that point the same direction.
Reasonable to act on. Individual response still varies, so the timing and the amount are yours to adjust.
Moderate
Consistent enough to be useful, but the size of the effect, the conditions it needs, or the people it was measured in leave real room to move.
Worth trying as an experiment you can reverse. Watch what happens over a fortnight, not a night.
Emerging
Early or narrow work. The idea is plausible and being actively studied, but it has not yet been tested widely enough to know how far it travels.
Interesting, not directive. We report it so you know it exists, not so you rearrange your evening around it.
Contested
Credible work disagrees. Different methods, populations, or definitions produce different answers, and the disagreement has not resolved.
Treat any confident claim in either direction with suspicion, including ours. We explain the disagreement rather than pick a side.
How a rating is decided
What counts as a source
We prefer, in roughly this order: systematic reviews and meta-analyses; randomised or controlled experimental work; well-conducted observational studies with a plausible mechanism; and consensus statements from professional sleep and circadian bodies.
We link directly to the source rather than to coverage of it, so you can check what it actually says. Where a source sits behind a paywall we say so and link the abstract.
We do not cite press releases, single-outlet news write-ups, or a product manufacturer describing its own product as evidence for that product.
How we judge quality
Beyond study design, we look at who was studied and whether the finding is likely to hold outside that group. Sleep research is heavily weighted towards young adults, university populations, and laboratory conditions with controlled light. A result from that setting is real, but it may be smaller or differently shaped in a household with children, a night shift, or a northern winter.
We look at effect size, not just whether a result reached significance. An effect that is reliably detectable but small enough to disappear inside normal night-to-night variation is not something we will tell you to rearrange your evening around.
We look for replication. One study is a finding. Several independent groups pointing the same way is a basis for advice.
What we do with disagreement
Where credible work disagrees, the page is rated contested and the disagreement is described. We do not average two opposing findings into a confident middle, and we do not quietly cite only the side we find more convincing.
Sometimes the disagreement is definitional — two studies measuring "sleep quality" in incompatible ways will reach incompatible conclusions. Where that is what is going on, we say so, because it changes what the argument is actually about.
Conflicts of interest
Restadian does not currently accept sponsored content, affiliate revenue, or paid product placement. If that changes, it will be disclosed on this page and on every page it affects.
When a cited study was funded by a party with a commercial interest in its outcome, we note that alongside the citation. Industry funding does not invalidate a study, but it is information a reader is entitled to have.
We do not rate a product category we sell into, because we do not sell into any.
What changes a rating
A rating moves up when independent replication arrives, when a mechanism that was inferred gets measured directly, or when a finding is confirmed in a population closer to the one reading the page.
A rating moves down when a replication fails, when a review finds the original effect was smaller than reported, or when a claim turns out to rest on fewer independent sources than it first appeared to.
When a rating changes, the guide records the change and the reasoning. Substantive changes are also published on the corrections page.
Review cadence
Every guide carries a review date and a next-review date, both visible on the page. The interval depends on how quickly the underlying evidence moves: fast-moving or contested topics are scheduled more frequently than settled mechanisms.
A review is not a proofread. It means the sources have been re-checked, newer work has been looked for, and the rating has been reconsidered against the definitions above. If nothing has changed, the review date still updates — that itself is useful information, because it tells you the page was checked rather than forgotten.
A page that passes its next-review date without being reviewed is flagged internally. We would rather mark a page as overdue than let it quietly age.
Think a rating is wrong?
That is a reasonable thing to think, and we would rather hear it. Point us at what we missed.