Researchers want to know if the concentration of ammonia in the James River is above the safe level for consumption. They take samples and develop a data set. Their null hypothesis is that the sample mean is > 6 (unsafe) and their alternative hypothesis is that the sample mean is < 6. Which of the following should they use in testing their hypothesis?

A) a one-tailed test

B) a two-tailed test

A - A one-tailed test

Explanation:

A one-tailed test is a statistical test that shows the sample mean would either be higher or lower than the population mean. It creates a relationship in a single direction such that the critical area is either greater or less than a stated value but not both. In a one-tailed test, null and alternative hypothesis have to be stated as if the tested sample is in a one-sided critical area, the alternative hypothesis is accepted.

In this scenario, the researchers' hypothesis take either > 6 or < 6 as the stated value. The result can only go in either of both direction, not both.