How To Test Hypotheses - Stat Trek

Find the P-value. The P-value is the probability of observing a sample statistic as extreme as the test statistic, assuming the null hypothesis is true.
  • For a one-tailed test. Find the probability of seeing a sample statistic greater than the absolute value of the test statistic. That is the P-value.
  • For a two-tailed test. Find the probability of seeing a sample statistic greater than the absolute value of the test statistic. Multiply that probability by 2 (to account for extreme values in the positive and negative tails of the sampling distribution). That is the P-value.

The P-value for a one-tailed test is half of the P-value for a two-tailed test.

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