Two tailed test意思

"Two-tailed test" is a term used in statistical hypothesis testing to describe a test where the critical region for rejecting the null hypothesis extends to both tails of the sampling distribution. This means that the test is set up to detect statistical significance in either direction, not just in one direction as in a one-tailed test.

In a two-tailed test, the researcher is interested in whether the mean of the population is different from the hypothesized value, but the direction of the difference is not specified in advance. For example, if the null hypothesis is that the population mean is equal to 100, a two-tailed test would allow for the possibility that the true mean is either greater than 100 or less than 100, and would provide evidence to reject the null hypothesis if the sample mean is far enough from 100 in either direction.

In contrast, a one-tailed test would only reject the null hypothesis if the sample mean was significantly different from 100 in one direction (e.g., greater than 100), but not if it was significantly different in the other direction (e.g., less than 100). Two-tailed tests are generally more conservative and less likely to find a significant result by chance, but they are also more robust against Type I errors (falsely rejecting a true null hypothesis).