Explain the advantages of one-tailed versus two-tailed testing. If one-tailed tests are more powerful, then why bother with two-tailed tests at all? Solution It depends on what the experimenter is interested in. Suppose a new drug is tested to see if it reduces blood pressure. The experimenter would use a one-tailed test. H0: No effect on the patient due to the new drug HA: New drug reduces blood pressure. If, on the other hand, one just wants to know whether there is a difference or there is no difference, he would use a two-tailed test. So, which is better to perform depends on what hypothesis the experimenter is testing..