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

a. Compare the mean drop in blood pressure for the high-dose group and the control

group. Use a ⫽ .05 and report the level of significance.

b. Estimate the size of the difference in the mean drop for the high-dose and control

groups using a 95 confidence interval.

c. Do the conditions required for the statistical techniques used in a and b appear to

be satisfied? Justify your answer. 6.51 Refer to Exercise 6.50. a. Compare the mean drop in blood pressure for the low-dose group and the control group. Use a ⫽ .05 and report the level of significance.

b. Estimate the size of the difference in the mean drop for the low-dose and control

groups using a 95 confidence interval.

c. Do the conditions required for the statistical techniques used in a and b appear to

be satisfied? Justify your answer. 6.52 Refer to Exercise 6.50. a. Compare the mean drop in blood pressure for the low-dose group and the high-dose group. Use a ⫽ .05 and report the level of significance.

b. Estimate the size of the difference in the mean drop for the low-dose and high-dose

groups using a 95 confidence interval.

c. Do the conditions required for the statistical techniques used in a and b appear to

be satisfied? Justify your answer. 6.53 In Exercises 6.50 – 6.52, we tested three sets of hypotheses using portions of the same data sets in each of the sets of hypotheses. Let the experiment-wide Type I error rate be defined as the probability of making at least one Type I error in testing any set of hypotheses using the data from the experiment.

a. If we tested each of the three sets of hypotheses at the .05 level, estimate the experiment-

wide Type I error rate.

b. Suggest a procedure by which we could be ensured that the experiment-wide Type I

error rate would be at most .05. Two-sample T for Low Dose vs Control N Mean StDev SE Mean Low Dose 20 3.8 44.0 9.8 Control 20 29.8 34.0 7.6 95 CI for mu Low Dose mu Control: 51.3, 0.8 T-Test mu Low Dose mu Control vs not : T 2.09 P 0.044 DF 35 -------------------------------------------------------------------------------- Two-sample T for High Dose vs Control N Mean StDev SE Mean High Dose 20 68.4 24.5 5.5 Control 20 29.8 34.0 7.6 95 CI for mu High Dose mu Control: 19.5, 57.6 T-Test mu High Dose mu Control vs not : T 4.12 P 0.0002 DF 34 -------------------------------------------------------------------------------- Two-sample T for Low Dose vs High Dose N Mean StDev SE Mean Low Dose 20 3.8 44.0 9.8 High Dose 20 68.4 24.5 5.5 95 CI for mu Low Dose mu High Dose: 87.6, 41.5 T-Test mu Low Dose mu High Dose vs not : T 5.73 P 0.0000 DF 29 Med. 6.54 To assess whether degreed nurses received a more comprehensive training than registered nurses, a study was designed to compare the two groups. The state nursing licensing board ran- domly selected 50 nurses from each group for evaluation. They were given the state licensing board examination and their scores are summarized in the following tables and graphs.

a. Can the licensing board conclude that the mean score of nurses who receive a BS in

nursing is higher than the mean score of registered nurses? Use a ⫽ .05. b. Report the approximated p-value for your test. c. Estimate the size of the difference in the mean scores of the two groups of nurses using a 95 confidence interval.

d. The mean test scores are considered to have a meaningful difference only if they differ

by more than 40 points. Is the observed difference in the mean scores a meaningful one? Pol. Sci. 6.55 All persons running for public office must report the amount of money spent during their campaign. Political scientists have contended that female candidates generally find it difficult to raise money and therefore spend less in their campaign than male candidates. Suppose the accompanying data represent the campaign expenditures of a randomly selected group of male and female candidates for the state legislature. Do the data support the claim that female candi- dates generally spend less in their campaigns for public office than male candidates? Campaign Expenditures in thousands of dollars Candidate 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

19 20

Female 169

206 257

294 252 283 240 207 230 183 298 269 256 277 300 126 318 184 252 305 Male 289 334 278 268 336 438 388 388 394 394 425 386 356 342 305 365 355 312 209 458

a. State the null and alternative hypotheses in

i. Plain English ii. Statistical terms or symbols

b. Estimate the size of the difference in campaign expenditures for female and male

candidates. c. Is the difference statistically significant at the .05 level? d. Is the difference of practical significance? 6.56 Refer to Exercise 6.55. What conditions must be satisfied in order to use the t procedures to analyze the data? Use the accompanying summary data and plot to determine whether these conditions have been satisfied for the data in Exercise 6.55. Two-Sample T-Test and Confidence Interval Two-sample T for Degreed vs RN N Mean StDev SE Mean Degreed 50 399.9 17.2 2.4 RN 50 354.7 30.9 4.4 95 CI for mu Degreed - mu RN: 35.3, 55.2 T-Test mu Degreed mu RN vs : T 9.04 P 0.0000 DF 76 450 400 350 300 Degreed nurses Registered nurses Examination scores Boxplots of degreed and registered nurses means are indicated by solid circles