After combining the data from the two depths, does there appear to be a difference in

6.48 Refer to Exercise 6.46. The researchers also examined the effect of depth on population abundance.

a. Plot the four data sets using side-by-side boxplots to demonstrate the effect of depth

on population abundance.

b. Separately for each depth, evaluate differences between the sites within and outside

the oil trajectory. Use a = .05. c. Are your conclusions at 40 m consistent with your conclusions at 100 m? 6.49 Refer to Exercises 6.46 – 6.48.

a. Discuss the veracity of the following statement: “The oil spill did not adversely affect the

population abundance; in fact, it appears to have increased the population abundance.”

b. A possible criticism of the study is that the six sites outside the oil trajectory were not

comparable in many aspects to the seven sites within the oil trajectory. Suppose that the researchers had data on population abundance at the seven within sites prior to the oil spill. What type of analysis could be used on these data to evaluate the effect of the oil spill on population abundance? What are some advantages to using these data rather than the data in Exercise 6.46?

c. What are some possible problems with using the before and after oil spill data in

assessing the effect of the spill on population abundance? Bio. 6.50 A study was conducted to evaluate the effectiveness of an antihypertensive product. Three groups of 20 rats each were randomly selected from a strain of hypertensive rats. The 20 rats in the first group were treated with a low dose of an antihypertensive product, the second group with a higher dose of the same product, and the third group with an inert control. Note that negative values represent increases in blood pressure. The accompanying computer output can be used to answer the following questions. Row Low Dose High Dose Control 1 45.1 54.2 18.2 2 59.8 89.1 17.2 3 58.1 89.6 34.8 4 23.7 98.8 3.2 5 64.9 107.3 42.9 6 12.1 65.1 27.2 7 10.5 75.6 42.6 8 42.5 52.0 10.0 9 48.5 50.2 102.3 10 1.7 80.9 61.0 11 65.4 92.6 33.1 12 17.5 55.3 55.1 13 22.1 103.2 84.6 14 15.4 45.4 40.3 15 96.5 70.9 30.5 16 27.7 29.7 18.5 17 16.7 40.3 29.3 18 39.5 73.3 19.7 19 4.2 21.0 37.2 20 41.3 73.2 48.8 ------------------------------------------- 100 50 –50 Low-dose group High-dose group 1 2 3 Control group Blood pressure Boxplot of blood pressure data