Assumptions Underlying the t Test
Assumptions Underlying the Independent-Samples t Test
Level of measurement. The criterion variable should be assessed on an interval-or ratio-level of measurement. The predictor variable should be a nominal-level variable that includes just two categories (i.e., two groups).
Independent observations. A given observation should not be dependent on any other observation in either group. In an experiment, you normally achieve this by drawing a sample and randomly assigning each participant to only one of the two treatment conditions. This assumption would be violated if a given participant contributed scores on the criterion variable under both treatment conditions.
The independence assumption is also violated when ...
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