The concentration of mercury in a lake has been monitored for a number of years. Measurements taken on a weekly basis yielded an average of 1.20 mg/m3 (milligrams per cubic meter) with a standard deviation of .32 mg/m3. Following an accident at a smelter on the shore of the lake, 15 measurements produced the following mercury concentrations.

a. Give a point estimate of the mean mercury concentration after the accident.
b. Construct a 95% confidence interval on the mean mercury concentration after the accident. Interpret this interval.
c. Is there sufficient evidence that the mean mercury concentration has increased since the accident? Use α = .05.
d. Assuming that the standard deviation of the mercury concentration is .32 mg/m3, calculate the power of the test to detect mercury concentrations of 1.28, 1.32, 1.36, and 1.40.

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1.60 177 16 108 107 179 134 107 1.45 159 143 2.07 116 0.85 2.11