Scenario D: Another team of investigators reviewed medical records to determine which military personnel among several basic training units had received a previous type of meningitis vaccine during training two decades ago. Two study groups were formed, those who had not received the vaccine and those who had. These were followed forward by record review throughout the duration of their active military service, and if they had a record of care through the VA system, these records were searched as well. The outcome of interest was the occurrence of any of a number of autoimmune diseases that were thought to have a possible association with the vaccine. In this study, of a vaccine group of 70, 4 individuals were found to have been diagnosed with lupus at some subsequent point in time. In the non- vaccine group of 105, only 2 individuals had that diagnosis 1. What type of study is this and what attributes makes it so? (See week 2 PPT): 2. What is the independent variable in this scenario, and what type is it? What is the dependent variable in this scenario, and what type is it? 3. State a null hypothesis. 4. What is the most appropriate measure of association to compare the rates of occurrence of autoimmune discase between the two groups and Why? Calculate that measure of association. 5. What is the most appropriate statistical test of significance of this measure of association and Why? Calculate the test result using the on-line calculator. Which test option should you use? What is the result? 6. Using the same on-line calculator as for problems #1 and #2, perform this test. What are the 2-tailed p- value results? 7. What do the results mean regarding the null hypothesis? Scenario E: Yet another team of investigators embarked on a long-term study to assess the impact of low versus high levels of blood cholesterol in Native Americans on subsequent occurrence of myocardial infarction. They recruited 100 patients from three Indian Health Service hospital systems, and divided them into two groups based on cholesterol LDL/HDL ratio (high ratio is bad) - 42 in the high group and 58 in the low group. By the end of the fifteen-year follow-up period, 16 in the high group and 7 in the low group had experienced a myocardial infarction. 1. What type of study is this and what makes it so? 2. What is the independent variable in this scenario, and what type is it? What is the dependent variable in this scenario, and what type is it? 3. State a null hypothesis. 4. What is the most appropriate measure of association to compare the rates of myocardial infarction in the two groups and Why? (See Week 2 PPT) Calculate that measure of association. What are the results? 5. Chi square w/o Yates correction is the most appropriate statistical test to test the significance of this measure of association. Why and what are the 2- tailed p-results? 6. What do the results mean in terms of the null hypothesis? Question F. From your readings, describe: 1. How the study design is selected. 2. How the measure of association is determined. 3. How the measure of significance is determined. 4. How interpretation of the results is accomplished
