Glossary
Evidence grade
A means a meta-analysis, a large cohort, or a randomized trial with a concrete number. B means a study exists, but the number is thin or the sample is small. C means experience or a widely repeated practice. Where this site replaced the source, the grade was reset to C instead of keeping the book’s grade.
RCT
A randomized controlled trial. People are assigned to groups by chance, and the groups are compared. The seat-belt 45% is an estimate from crash data, not an RCT.
Meta-analysis
A method that pools several studies into one estimate. The helmet Cochrane review and the 94 if-then tests are meta-analyses.
Relative risk
The rate of an event in one group divided by the rate in another. Below 1 means the event was less common. An odds ratio is related, and it is not the same number.
Value tier
The original author’s judgment. “Best” means no money, little time, almost no willpower, and a large payoff. It is separate from the evidence grade.
Rough estimate
Yen and dollar figures are rebuilt from local shelf prices. An editor rechecks them before launch. They are not a fixed price.