t-test

A t-test checks whether the mean (平均數) of a group, or the difference between two groups’ means, is distinguishable from a baseline given the noise — the everyday tool for “is group A’s average really different from group B’s?” It produces a t-statistic and a p-value.

It is built for numeric, roughly bell-shaped data and uses the Student’s t-distribution, which has fatter tails than the normal to account for the extra uncertainty of estimating the standard deviation from a small sample. With large samples it nearly matches a normal z-test; with skewed data or outliers (離群值) it can mislead, so check your data or use a robust alternative.