Question

Sludge is a dried product remaining from processed sewage and is often used as a fertilizer on agriculture crops. If the sludge contains a high concentration of certain heavy metals, such as nickel, the nickel may reach such a concentration in the crops that it becomes a danger to the consumer of the crops. A new method of processing sewage has been developed, and an experiment is conducted to evaluate its effectiveness in removing heavy metals. Sewage of a known concentration of nickel is treated using both the new and the old methods. One hundred tomato plants were randomly assigned to pots containing sewage sludge processed by one of the two methods. The tomatoes harvested from the plants were evaluated to determine if the nickel was at a toxic level. The results are as follows:
a. For both treatments, place 95% confidence intervals on the proportions of plants that would have a toxic level of nickel.
b. Is there significant evidence (ɑ = .05) that the new treatment would produce a lower proportion of plants having a toxic level of nickel compared to the old treatment?
c. Use the Fisher Exact test to test the research hypothesis that the new treatment would produce a lower proportion of plants having a toxic level of nickel compared to the old treatment. Compare your conclusions with the conclusions reached in part (b).
d. Place a 95% confidence interval on the difference in the two proportions.


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  • CreatedNovember 21, 2015
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