# Two-Tailed Test

How to decide whether your test should be one-tailed or two-tailed/directional or non-directional. Gives an example of each type, with an explanation of why it is/is not directional.

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#### Solution Preview

A two-tailed (non-directional) test tests only whether there is a difference between two or more groups/samples/means. A one-tailed (directional) test also tests for differences between groups/samples/means, but it tests for a directional difference between them (ie. whether one is bigger/smaller than another).

Example 1.

The mean grade in last year's Introductory Statistics class was 72, with a standard deviation of 6.2. This year, a new professor taught the course, and the mean grade was 81, ...

#### Solution Summary

How to decide whether your test should be one-tailed or two-tailed/directional or non-directional. Gives an example of each type, with an explanation of why it is/is not directional.