- Appeal to nature
- The assumption that something is safe or good because it occurs in nature, and suspect because it was manufactured. It is a shortcut about origin, not a statement about how a substance behaves.
- Correlation
- A statistical association between two things. It means they move together in the data; on its own it says nothing about whether one causes the other, or whether a third factor drives both.
- Confounder
- A hidden factor linked to both the thing being studied and the outcome, capable of producing an association that has nothing to do with cause. The reason observational findings are reported cautiously.
- Effect size
- How large a difference is, as opposed to whether one exists at all. A result can be statistically detectable and still be too small to notice in an ordinary life.
- Meta-analysis
- A study of studies: results from multiple investigations pooled and weighted to see what the whole literature suggests. Generally more informative than any single trial in it.
- Observational study
- Research that watches what people already do rather than assigning them to do it. Useful for spotting patterns and generating questions; limited in what it can establish about cause.
- Placebo effect
- Improvement that follows an inert treatment, driven by expectation, attention, and the natural course of the complaint. It is why trials compare against a placebo rather than against nothing.
- Publication bias
- The tendency for striking positive results to reach print while null results stay in a drawer. It can make a body of evidence look more decisive than it is.
- Randomized controlled trial (RCT)
- A study that assigns participants to groups by chance, so that unmeasured differences are distributed evenly. The design best suited to questions about cause, though not always practical.
- Regression to the mean
- The tendency for an unusual measurement to be closer to average when taken again. It quietly manufactures the appearance of improvement whenever people act at their worst moment.
- Replication
- An independent attempt to repeat a study and obtain the same result. A finding that has been replicated is knowledge; a finding that has not is a lead.
- Selection bias
- Distortion introduced by how a sample was gathered — when the people, cases, or photographs included differ systematically from the ones left out.
- Statistical significance
- A conventional threshold indicating a result is unlikely to have arisen from chance alone, under the study's assumptions. It speaks to noise, not to importance or to size.
- Structure/function claim
- A permitted phrasing on some product labels describing an effect on the body's normal structure or function — worded to avoid stating that a product treats or prevents any disease.
- %DV (Percent Daily Value)
- How much a nutrient in one serving contributes to a reference intake built for a hypothetical average adult. A comparison benchmark between products, not a personal target.
- Serving size
- A standardized amount used so that two products can be compared on the same footing. It is a measuring convention, not a recommendation about how much to eat.