Fish absorb mercury as water passes through their gills, and too much mercury makes the fish unfit for human consumption. In 1994, the state of Maine issued a health advisory warning that people should be careful about eating fish from Maine lakes because of the high levels of mercury. Before the warning, data on the status of Maine lakes were collected by the U.S. Environmental Protection Agency (EPA) working with the state. Fish were taken from a random sample of lakes, and their mercury content was measured in parts per million (ppm). Display 9.43 shows a subset of those data from a random sample of 35 lakes.
Â a. Are there any problems with computing a confidence interval estimate of the mean mercury levels in fish for the lakes of Maine using the values in the table? If so, how do you recommend handling the analysis?
Â b. One newspaper headline proclaimed, â€œMercury: Maine Fish Are Contaminated by this Deadly Poison.â€ Most states consider mercury levels of 0.5 ppm as the borderline for issuing a health advisory. Does it appear that, on average, Maine lakes deserved the headline? Justify your answer statistically.