Hurricanes Katrina and Rita caused the flooding of large parts of New Orleans, leaving behind large amounts of new sediment. Before the hurricanes, the soils in New Orleans were known to have high concentrations of lead, which is a dangerous environmental toxin. Fortysix sites had been monitored before the hurricanes for soil lead content, as measured in mg/kg, and the soil from each of these sites was measured again after the hurricanes (Zahran et al. 2010). The data given below show the log of the ratio of the soil lead content after the hurricanes and the soil lead content before the hurricanes—we’ll call this variable the “change in soil lead.” (Therefore, numbers less than zero show a reduction in soil lead content after the hurricanes, and numbers greater than zero show increases.) This log ratio has an approximately normal distribution.

n=46, ΣY=−12.62, ΣY²=18.4606

a. Draw a graph of the data, following recommended principles of good graph design (Chapter 2). What trend is suggested?

b. Determine the 95% confidence interval for the mean change in soil lead. Describe in words what the nature of that change is. Is an increase in soil lead consistent with the data? Is a decrease in soil lead consistent?

c. Test whether mean soil lead changed after the hurricanes.

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-0.83,-0.83,-0.18.-0.18, 0.14,0.14, -1.46,-1.46, -0.48,-0.48, -1.04, -1.04, 0.25,0.25, -0.34,-0.34, -0.81,-0.81, -0.83.-0.83,-0.60,-0.60, 0.34,0.34, -0.75,-0.75, 0.37,0.37, 0.26.0.26, 0.46,0.46, -0.03.-0.03, -0.32,-0.32, -0.53,-0.53, -1.55,-1.55, -0.90,-0.90, -0.95,-0.95, -0.13.-0.13, -0.75,-0.75, 0.59,0.59, -0.06.-0.06, 0.39,0.39, -0.40. -0.40, -0.84,-0.84, -0.56,-0.56, 0.44.0.44, 0.18,0.18, 0.28,0.28,