Final Exam OLD VERSION DO NOT USE

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Instructions

• This exam is to be taken under conditions given by the Vanderbilt honor code. Do not ask for help for questions from anyone except the instructors. We will reply through the discussion board so everyone has the opportunity to benefit equally from our responses.
• Include the statement of the Vanderbilt honor code on your work: "I pledge on my honor that I have neither given nor received unauthorized aid on this assignment."
• Exams are due by Monday, 4/28, at 9 AM either by email (to Chris; mailto:james.c.slaughter@vanderbilt.edu) or directly handed to me in my office (T-2319, MCN). I will be in my office from 7 to 9, but I have a meeting at 9:05 on Monday and Frank will be out of town, so exams may not be turned in late.

Problem 1

Consider the following general research question: Does increasing fiber consumption have health benefits?

1. Refine this general research question into a specific question you believe would be feasible, interesting, ethical, and relevant to study. Write the question in a single sentence that describes the predictor, outcomes, and population you want to study.
2. Describe the optimal study design for answering your specific research question.
3. Explain why your chosen design is better that other designs. Make specific references to at least one other potential study design.
4. Describe the type of preliminary information you would need to collect in order to perform a power/sample size calculation for your study. How would you get this information?

Note that there are many possible answers to each of these questions. More credit will be given for answers that demonstrate a better understanding of study design issues discussed in the course.

Problem 2

1. Show that if: then
2. Why do we use the logit transformation to model binary outcomes?

Problem 3

An investigator first computes the percent change in a measurement from baseline to steady state, for each animal. Then she computes the mean percent change over animals. Name at least two things the investigator did wrong.

Problem 4

Use the igp304.final.data.xls dataset to answer the following questions

1. Perform a descriptive analysis of the variables in the raw dataset provided. Turn in one table, one figure, and an accompanying paragraph that describes the dataset. Identify any extreme outlying values that you feel should be removed from subsequent analyses.
2. Is there a statistically significant difference in the tumor rate between knockout and wild-type mice? Provide a one-sentence answer that includes a P Value, the test used, and the tumor percentage for each group. Note: wild=1 for wild-type and wild=0 for knockout; tumor 0=none, 1=one or more.
3. Is there a statistically significant difference between the baseline size of those randomized to Drug A and those randomized to Drug B? Provide 95% confidence intervals and a P value. Note SIZE1=baseline, Drug A=1, B=2.
   • Hint: You may find that rearranging the dataset will be easier to analyze in your software package. See igp304.final.size.xls where SIZEA = Baseline size, drug A and SIZEB = baseline size, Drug B. Similar rearrangements may be helpful on other questions.
4. Is there a significant change in the size from baseline to the size at 30 days after baseline in this study? Note: size1=baseline, size2=at 30 days. Provide 95% CI for the change in size, a P value, and the test used.
5. Is the LOS statistically different between wild-type and knockout mice? Provide the median for each group, a P value, and the test used. Note: LOS=a continuous marker of disease severity
6. What is the odds ratio of wild-type vs. knockout developing a tumor? Provide a P value and 95% confidence interval for the odds ratio.
7. Is there a statistically significant association between age and baseline size (size1)? Provide a P value and describe the test used.
8. Based on these preliminary results, a larger study is being planned. A new drug has been developed that is thought to be able to have 50% fewer tumors than Drug A had in this study. How many mice would be required in each of 2 groups of a randomized trial to have 90% power of detecting a statistically significant difference at the 0.05 level assuming one group was expected to have the percent of tumors found with Drug A in this study and the other drug is expected to have half as many complications? Provide sufficient information in your answer so that a biostatistician could reproduce your answer.

Problem 5

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