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Bio Statistics week 6




Question;Problem;1: A clinical trial evaluates a new compound;designed to improve wound healing in trauma patients. The new compound is compared against a placebo. After treatment for 5 days with the new;compound or placebo the extent of wound healing is measured and the data are;shown below. Is there a difference in the extent of wound healing by treatment? (Hint;Are treatment and the percent wound healing independent?) Run the appropriate test at a 5% level of;significance. Based on this result, does;the new treatment appear to be any different from the placebo?;Problem;2: The following data were collected in an;experiment designed to investigate the impact of different positions of the;mother during ultrasound on fetal heart rate.;Fetal heart rate is measured by ultrasound in beats per minute. The study includes 20 women who are assigned;to one position and have the fetal heart rate measured in that position. Each woman is between 28-32 weeks;gestation. The data are shown;below. Is there a significant difference;in mean fetal heart rates by position?;Run the test at a 5% level of significance. Based on this result, does;position appear to effect fetal heart rate?;Problem;3: A clinical trial is conducted to compare an;experimental medication to placebo to reduce the symptoms of asthma. Two hundred participants are enrolled in the;study and randomized to receive either the experimental medication or;placebo. The primary outcome is;self-reported change of symptoms. The;data are shown below. Is there a difference in change in symptoms by treatment;group? Run the appropriate test at a 5%;level of significance. Based on this result, does there appear to be a;difference between the experimental medication and the placebo?;Problem;4: Suppose a hypertension trial is mounted and 18;participants are randomly assigned to one of the comparison treatments. Each participant takes the assigned;medication and their systolic blood pressure (SBP) is recorded after 6 months;on the assigned treatment. The data are;given below. Is there a difference in mean SBP among treatments? Run the appropriate test at?= 0.05. Based on this result, does the new medication;appear to be any different from the standard treatment and the placebo?;Problem;5: An investigator wants to estimate caffeine;consumption in high school students. How;many students would be required to ensure that a 95% confidence interval;estimate for the mean caffeine intake (measured in mg) is within 15 mg of the;true mean? Assume that the standard;deviation in caffeine intake is 68 mg.;Problem;6: Consider the study proposed in problem 5. How many students would be required to;estimate the proportion of students who consume coffee? Suppose we want the estimate to be within 5%;of the true proportion with 95% confidence.;Problem;7: A crossover trial is planned to evaluate the;impact of an educational intervention program to reduce alcohol consumption in;patients determined to be at risk for alcohol problems. The parameter of interest is the mean;reduction in number of drinks per day. To get the desired margin of error;statisticians determine the necessary sample size is n = 150. However;researchers anticipate that 20% of the participants will drop out over the;course of follow-up. How many participants should be enrolled?;Problem;8: The mean body mass index (BMI) for boys age 12;is 23.6. An investigator wants to test;if the BMI is higher in 12-year-old boys living in New York City. How many boys are needed to ensure that a;two-sided test of hypothesis has 80% power to detect a difference in BMI of 2;units? Assume that the standard;deviation in BMI is 5.7.;Problem;9: Recently it has been observed that HIV-infected;patients develop peripheral lypoatrophy while on potent antiretroviral;therapy. A clinical trial is planned to;determine if a new chemical will improve this condition. In the trial, participants will be randomized;to receive the new chemical or a placebo and changes from baseline in;subcutaneous adipose cross-sectional area as measured by CT scan will be;calculated after 24 weeks of treatment.;Investigators hope to show that the increases in patients receiving the;chemical are greater than the increases in patients receiving the placebo. They hypothesize that the participants;assigned to the chemical arm will exhibit a mean change of 30% and the;participants assigned to the placebo arm will exhibit a mean change of 0%. Prior literature suggests that the standard;deviation of the changes will be 57% in both arms. How many participants are needed to ensure;80% power? Assume?=0.05, equal numbers;in each group, and that 20% of the participants will drop out over the course;of follow-up.;Problem;10: In the worksheet CI Simulation of the Excel;workbook Chapter 8, change the population parameters and the confidence level;to assorted values. Each time press the F9 key several times to repeat the;simulation. Compare the confidence level to the proportion of confidence;intervals that contain?. In your own words, state what the;confidence level means when constructing a confidence interval estimate of a;population parameter.


Paper#62284 | Written in 18-Jul-2015

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