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Statistics vocabulary · Hypothesis Testing

Two-tailed test

Meaning in statistics, with examples

nounCommon term

In statistics, two-tailed test means: A hypothesis test that looks for a difference in either direction, so the rejection region is split between both ends (tails) of the distribution.

In Turkish: çift yönlü test, iki kuyruklu test

How it is used

The default in most research, also called a two-sided test. A one-tailed (one-sided) test checks only one direction and must be justified before seeing the data; switching to a one-tailed test afterwards to get p < .05 is poor practice.

Example sentences

  1. All p-values are from two-tailed tests.

  2. We chose a two-tailed test because the new process could make delivery times either shorter or longer.

Common collocations

  • two-tailed p-value
  • one-tailed test
  • two-sided test
  • two-tailed at α = .05
  • alternative hypothesisThe statement that there is a real effect, difference or relationship; it is the claim a researcher usually expects, and the data support it when they give strong evidence against the null hypothesis.
  • p-valueThe probability of getting a result at least as extreme as the one observed if the null hypothesis were true; a small value means the data would be surprising under the null.
  • significance levelThe threshold, chosen before a test, below which a p-value is treated as statistically significant; it is also the accepted risk of a Type I error.
  • null hypothesisThe default claim in a statistical test that there is no effect, no difference or no relationship; the test checks whether the data give enough evidence against it.

More terms: Hypothesis Testing

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