Sign Test
A non-parametric test for paired data using the binomial distribution, testing H₀: median difference = 0 by comparing the number of positive differences to a binomial B(n, 0.5) distribution.
Real World
A physiotherapist tests whether a new stretching programme improves flexibility by measuring patients before and after, using the sign test because the improvement data is not normally distributed.
Exam Focus
Remember to exclude zero differences from n before looking up the critical value — forgetting this changes the conclusion.
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