Meta-Analysis

A pooled number is powerful and dangerous. Done on comparable studies it sharpens the truth; done on studies that measured different things it manufactures a precise-looking lie. The judgment this skill enforces is not "how do I average these" — it is "should these be averaged at all?"

When to use

Whenever the agent is tempted to report one effect size (a risk ratio, an odds ratio, a mean difference, an HR) drawn from more than one study.

The rule

Only pool comparable primary studies. When they are not comparable, show them individually and say why.

Before combining, every study in the pool must share:

1. Population — same clinical group, not "adults" vs "elderly with comorbidity" flattened together.
2. Intervention / exposure — same drug, comparable dose and route; same exposure definition.
3. Comparator — placebo vs active control are different questions; do not mix them into one pool.
4. Outcome and its measure — the same endpoint, defined and measured the same way, on the same scale.
5. Design tier — do not pool RCTs with observational studies into a single estimate. Report them in separate strata.