Question

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. Suppose 44 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 hurricane -- we will 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.) 0.21−0.950.390.170.64−0.130.260.34−0.81−1.55−0.750.44−1.240.57−0.32−0.83−0.340.25−0.840.13−0.53−0.36−0.75−0.510.280.18−0.060.46−0.78−0.83−0.56−0.03−0.41−1.04−0.4−0.63−0.180.49−0.26−0.90.590.14−0.60.37 Zahran, S., H. W. Mielke, C. R. Gonzales, E. T. Powell, and S. Weiler (2010): New Orleans before and after hurricanes Katrina/Rita: A quasi-experiment of the association between soil lead and children's blood lead. Environmental Science and Technology 44, 4433--4440. (a) Create a graph of the data, following recommended principles of good graph design. Which of the following best describes the distribution? A. Bimodal, centred at a value above zero. B. Uniform (that is, flat). C. Bimodal, centred at a value below zero. D. Unimodal, centred at a value below zero. E. Unimodal, centred at a value above zero. (b) Determine a 95% confidence interval for the mean change in soil lead. Give your bounds to three decimal places. ( , ) (c) To test the null hypothesis that mean soil lead did not change after the hurricanes, provide your test statistic to three decimal places. (d) Assuming you test your null hypothesis at the 5% significance level, which of the following would you conclude? A. There is no evidence to reject the claim that mean soil lead did not change after the hurricanes. B. There is evidence to support the claim that mean soil lead concentration declined after the hurricanes. C. There is evidence to support the claim that mean soil lead concentration increased after the hurricanes.

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. Suppose 44 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 hurricane -- we will 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.)
0.21−0.950.390.170.64−0.130.260.34−0.81−1.55−0.750.44−1.240.57−0.32−0.83−0.340.25−0.840.13−0.53−0.36−0.75−0.510.280.18−0.060.46−0.78−0.83−0.56−0.03−0.41−1.04−0.4−0.63−0.180.49−0.26−0.90.590.14−0.60.37
Zahran, S., H. W. Mielke, C. R. Gonzales, E. T. Powell, and S.
Weiler (2010): New Orleans before and after hurricanes
Katrina/Rita: A quasi-experiment of the association between soil
lead and children's blood lead.
Environmental Science and Technology
44, 4433--4440.
(a) Create a graph of the data, following
recommended principles of good graph design. Which of the following
best describes the distribution?
A. Bimodal, centred at a value above zero.
B. Uniform (that is, flat).
C. Bimodal, centred at a value below zero.
D. Unimodal, centred at a value below zero.
E. Unimodal, centred at a value above zero.
(b) Determine a 95% confidence interval for the
mean change in soil lead. Give your bounds to three decimal
places.
( , )
(c) To test the null hypothesis that mean soil
lead did not change after the hurricanes, provide your test
statistic to three decimal places.
(d) Assuming you test your null hypothesis at the
5% significance level, which of the following would you
conclude?
A. There is no evidence to reject the claim that
mean soil lead did not change after the hurricanes.
B. There is evidence to support the claim that
mean soil lead concentration declined after the hurricanes.
C. There is evidence to support the claim that
mean soil lead concentration increased after the hurricanes.

Added by Elizabeth T.

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