Species n x Mugil liza 56 9.15 1.27 Pogonias cromis 61 3.08 1.71
Heavy-metal pollution of various ecosystems is a serious environmental threat, in part because of the potential transference of hazardous substances to humans via food. The article “Cadmium, Zinc, and Total Mercury Levels in the Tissues of Several Fish Species from La Plata River Estuary, Argentina” (Environmental Monitoring and Assessment, 1993: 119–130) reported the following summary data on zinc concentration ( g@g) in the liver of fish:
a. Calculate a 95% two-sided confidence interval for population mean concentration for the Mugil liza species.
b. Calculate a 99% two-sided confidence interval for population mean concentration for the Pogonias cromis species. Why is this interval wider than the interval of part (a) even though it is based on a somewhat larger
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