Physical Sciences

In a study of several Chesapeake Bay tributaries, a random sample of nontidal freshwater locations on the Patuxent River was obtained. The total arsenic concentration was measured at each location (in mg/L), and the data are given in the following table.

Suppose the distribution of arsenic concentrations is continuous and symmetric and that the safe level of arsenic concentration is 0.30 μg/L.

a. Conduct a sign test to determine whether there is any evidence that the median arsenic concentration in freshwater locations is greater than 0.30 mg/L. Use a = 0.05.

b. Conduct a signed-rank test to determine whether there is any evidence that the median arsenic concentration in freshwater locations is greater than 0.30 mg/L. Use a = 0.05.

c. Compare your conclusions in parts (a) and (b). Which test do you think is more accurate? Why?