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# Bio Statistics week 6

Question # 00012234
Subject: Statistics
Due on: 04/29/2014
Posted On: 04/13/2014 04:04 PM

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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.

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#### Bio Statistics week 6

Tutorial # 00011793
Posted On: 04/13/2014 04:06 PM
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