How to tell if a hypothesis test is left or right tailed

Step 1. Set up hypotheses and select the level of significance α. H 0: Null hypothesis (no change, no difference); H 1: Research hypothesis (investigator's belief); α =0.05.

Statistics Examples

For a left tailed test we need to check if the test statistic (TS) is smaller than the critical value (CV). If the test statistic is smaller the critical value, the test statistic is in the rejection region.

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Left Tailed Test or Right Tailed Test ? How to Decide

If your alternative is that the mean is not zero, then you do a two-tailed test. If your alternative is that the mean is greater than zero (or less than zero, either one) you do a one-tailed test. But