Marked Assignment 2, EPID6420 Epidemiology A Semester 1, 2017 This assessment task contributes 15% towards your total marks. Complete the answers (show your working for all calculations, not just the answer) and submit them to Turnitin via blackboard by the nominated due date. We do not expect, or want you to write a mini essay for each response. Succinct answers which cover all the relevant points are desirable. However, make sure you show the formulae and all workings for any calculations undertaken. This may allow us to still allocate you marks even if your final answer was incorrect (in the unlikely event this would occur!). For all calculations, use up to 2 decimal point.
Question 1 6 marks A case control study among 2000 individuals was conducted to determine the association between cigarette smoking and coronary heart disease. Out of the study subjects, 50% had coronary heart disease; 70% of the cases were smokers and 60% of the controls were non-smokers.
1. Draw the 2 x 2 table to explore the relationship between coronary heart disease and cigarette smoking. (2 marks)
2. Calculate the crude odds ratio and explain its exact meaning. (2 marks) Data were further stratified according to gender of the study subjects: Males Coronary heart disease Cigarette smoking Cases Controls Exposed 520 140 Unexposed 180 360 Total 700 500 Females Coronary heart disease Cigarette smoking Cases Controls Exposed 180 260 Unexposed 120 240 Total 300 500 Using this information, explain whether gender is a confounder or effect modifier? (2 marks)
Question 2 9 Marks A large randomized controlled trial is carried out to determine the effect of pravastatin, a cholesterol lowering medication, in elderly people (>65 years old) at risk of cardiovascular disease, i.e. heart attacks and strokes. Out of 23 770 individuals assessed at various family practices, only 7056 were eligible and agreed to participate. These were entered into a “run-in” period, in which they were given placebo tablets for 4 weeks. Those who were not compliant in taking their medicine were dropped from the trial, leaving 5804 patients to be randomized. 2913 were assigned placebo, and 2891 were assigned pravastatin.
Over the next 3 years, 650 and 725 people discontinued their medication, respectively (lack of compliance), but all participants continued to be followed for fatal and non-fatal heart attacks, as well as fatal and non-fatal strokes. The authors perform an intention to treat analysis, with all cardiovascular events being the primary endpoint (combined fatal and non-fatal heart attacks and fatal and non-fatal strokes). In the placebo group, 473 reached a primary endpoint vs. 408 in the pravastatin group.
1. Draw the 2 x 2 table for all cardiovascular outcomes combined (fatal and non-fatal heart attack and fatal and non-fatal stroke all combined). (1 mark) 2. What is the absolute risk of all cardiovascular outcomes in the placebo and drug group? Explain this in words. (2 marks)
3. What is the absolute risk reduction in all cardiovascular outcomes in the drug group vs the placebo group? Explain this in words. (1 mark)
4. What is the relative risk reduction in all cardiovascular outcomes in the drug group vs the placebo group? Explain this in words. (1 mark)
5. What is the number needed to treat? Explain this in words. (2 marks)
6. What effect does the differential lack of compliance have? What is the direction of this bias? How does this affect internal validity? (2 mark) Biology homework help