p-value
MCAT glossary · Critical Analysis & Reasoning Skills
Definition
The probability of a result at least as extreme as that observed, assuming the null hypothesis is true.
p-value in plain English
A p-value helps you judge whether a result is real or just luck. It answers: 'If nothing special were going on, how often would I see a result this surprising by pure chance?' A small p-value (say under 0.05) means 'this would rarely happen by luck alone,' so people take the result seriously. It's like flipping a coin and getting heads 9 times out of 10 — a low p-value is the math saying 'a fair coin almost never does that, so something's probably up.'
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