The *t*-test for dependent means (also called a repeated-measures
*t*-test, paired samples *t*-test, matched pairs
*t*-test and matched samples *t*-test) is used to compare the means of two sets of scores
that are directly related to each other. So, for example, it could be used to test
whether subjects' galvanic skin responses are different under two conditions
- first, on exposure to a photograph of a beach scene; second, on exposure to a
photograph of a spider.

*Requirements*

- The data is normally distributed
- Scale of measurement should be interval or ratio
- The two sets of scores are paired or matched in some way

*Null Hypothesis*

H_{0}: U_{D} = U_{1 }- U_{2} = 0, where U_{D}
equals the mean of the population of difference scores across the two measurements.

*Equation*