Paired T-Test

The Paired t-test is a parametric test for comparing the means of two variables from the same groups.

Assumptions
The assumptions of this test are as follows:


 * 1) The difference between the two variables (Var2 - Var1) must be normally distributed.


 * 1) The variables must be at least at the interval level.

Non-Parametric Equivalent
The non-parametric equivalent of this test is the Wilcoxon Signed Rank Test.

Example
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In SPSS
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Writing up
A paired-samples t-test was conducted to compare hours of sleep in caffeine and no caffeine conditions. There was a significant difference in the scores for caffeine (M=5.4, SD=1.14) and no caffeine (M=9.4, SD=1.14) conditions; t(4)=-5.66, p = 0.005. These results suggest that caffeine really does have an hours slept. Specifically, our results suggest that when humans consume caffeine, the number of hours they sleep decreases.