<P> The t - test is any statistical hypothesis test in which the test statistic follows a Student's t - distribution under the null hypothesis . </P> <P> A t - test is most commonly applied when the test statistic would follow a normal distribution if the value of a scaling term in the test statistic were known . When the scaling term is unknown and is replaced by an estimate based on the data, the test statistics (under certain conditions) follow a Student's t distribution . The t - test can be used, for example, to determine if two sets of data are significantly different from each other . </P> <P> The t - statistic was introduced in 1908 by William Sealy Gosset, a chemist working for the Guinness brewery in Dublin, Ireland . "Student" was his pen name . </P>

When should the matched pairs t-test be used
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