If there is only one way to disprove a null hypothesis, the statistical test is one-tailed. EX: â€œThere is either no correlation or a negative correlation between age at first dental visit and DMF at age 30â€ is a one-tailed test â€“ there is only one way to disprove it (finding a positive correlation). The operational significance of a one-tail test comes in determining the p-value from the test statistic. One-tail tests have lower p-values for a given test statistic than two-tail tests. [See null hypothesis, two-tailed test

a standard statistical methodology used when there is prior evidence that the effect of an agent is likely to be in one specific direction

hypothesis test in which the rejection region consists entirely of either large values or small values of the test statistic. Such a test is appropriate against one-sided alternatives. (Note, however, that or chi-squared tests can be one-tailed against two-sided alternatives.)

a statistical test in which the critical region for rejecting the null hypothesis falls in one direction of the probability distribution

A test in which the alternative hypothesis specifies a deviation from the null hypothesis in one direction only. The critical region is located in one end of the distribution of the test statistic. It is also called a directional test.