Non-clinical sciences/Stats & evidence · Inference

p-value & confidence interval

What it means

p = probability of a result at least this extreme if the null hypothesis were true (p<0.05 is the usual threshold; it is NOT the probability the hypothesis is true). 95% CI = range that would contain the true value in 95% of repeated studies; a CI crossing the null (1 for RR/OR, 0 for differences) = non-significant. Wider CI = less precision (narrows with larger n).

Worked example

RR 0.8 (95% CI 0.6–1.05): not statistically significant because the interval crosses 1.

In the exam

A result is reported as non-significant because its 95% confidence interval for the risk ratio includes the value 1.

What settles it

A CI shows effect size AND precision; a bare p-value shows only whether it crossed a threshold. p<0.05 ≠ 'clinically important'.

Classically confused with

NNT & NNH

Source: StatPearls