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Applied Biostatistics Final Exam




1. The following are body mass index (BMI) scores measured in 12 patients who are free of diabetes and participating in a study;of risk factors for obesity. Body mass index is measured as the ratio of weight in kilograms to height in meters squared.;Generate a 95% confidence interval estimate of the true BMI. 25 27 31 33 26 28 38 41 24 32 35 40;2. Consider the data in Problem #1. How many subjects would be needed to ensure that a 95% confidence interval estimate of;BMI had a margin of error not exceeding 2 units?;3. A clinical trial is run to investigate the effectiveness of an experimental drug in reducing preterm delivery to a drug considered;standard care and to placebo. Pregnant women are enrolled and randomly assigned to receive either the experimental drug, the;standard drug or placebo. Women are followed through delivery and classified as delivering preterm (< 37 weeks) or not. The data;are shown below.;Preterm Delivery;Experimental Drug;Standard Drug;Placebo;Yes;17;23;35;No;83;77;65;Is there a statistically significant difference in the proportions of women delivering preterm among the three treatment groups?;Run the test at a 5% level of significance.;4. Consider the data presented in problem #4. Previous studies have shown that approximately 32% of women deliver prematurely;without treatment. Is the proportion of women delivering prematurely significantly higher in the placebo group? Run the test at a;5% level of significance.;5. A study is run comparing HDL cholesterol levels between men who exercise regularly and those who do not. The data are shown;below.;Regular Exercise;N;Mean;Std Dev;Yes;35;48.5;12.5;No;120;56.9;11.9;6. A clinical trial is run to assess the effects of different forms of regular exercise on HDL levels in persons between the ages of 18 and;29. Participants in the study are randomly assigned to one of three exercise groups - Weight training, Aerobic exercise or;Stretching/Yoga ? and instructed to follow the program for 8 weeks. Their HDL levels are measured after 8 weeks and are;summarized below.;Exercise Group;N;Mean;Std Dev;Weight Training;20;49.7;10.2;Aerobic Exercise;20;43.1;11.1;Stretching/Yoga;20;57.0;12.5;Is there a significant difference in mean HDL levels among the exercise groups? Run the test at a;5% level of significance. HINT: SSwithin = 21,860.;7. Consider again the data in problem #6. Suppose that in the aerobic exercise group we also measured the number of hours of aerobic;exercise per week and the mean is 5.2 hours with a standard deviation of 2.1 hours. The sample correlation is -0.42.;a) Is there evidence of a significant correlation between number of hours of exercise per week and HDL cholesterol level? Run the;test at a 5% level of significance.;b) Estimate the equation of the regression line that best describes the relationship between number of hours of exercise per week;and HDL cholesterol level (Assume that the dependent variable is HDL level).;c) Estimate the HDL level for a person who exercises 7 hours per week.;d) Estimate the HDL level for a person who does not exercise.;8. The following data were collected in a clinical trial to compare a new drug to a placebo for its effectiveness in lowering total serum;cholesterol. Generate a 95% confidence interval for the difference in mean total cholesterol levels between treatments.;New Drug;Placebo;Total Sample;(n=75);(n=75);(n=150);Mean (SD) Total Serum;Cholesterol;% Patients with Total;Cholesterol < 200;185.0 (24.5);204.3 (21.8);194.7 (23.2);78.0%;65.0%;71.5%;9. A small pilot study is conducted to investigate the effect of a nutritional supplement on total body weight. Six participants agree to;take the nutritional supplement. To assess its effect on body weight, weights are measured before starting the supplementation and;then after 6 weeks. The data are shown below. Is there a significant increase in body weight following supplementation? Run the;test at a 5% level of significance.;Subject;Initial Weight;Weight after 6;Weeks;1;155;157;2;142;145;3;176;180;4;180;175;5;210;209;6;125;126;10. Answer True or False to each of the following;a) The margin of error is always greater than or equal to the standard error.;b) If a test is run and p=0.0356, then we can reject H0 at?=0.01.;c) If a 95% CI for the difference in two independent means is (-4.5 to 2.1), then the point estimate is -2.1.;d) If a 95% CI for the difference in two independent means is (2.1 to 4.5), there is no significant difference in means.


Paper#35099 | Written in 18-Jul-2015

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