Epidemiology-Biostatistics Small Group Session 1: Evaluating a Randomized Controlled Trial
Outside Preparation: Due for Small Group #1
- Researchers prospectively studied multiple exposures and outcomes in 200 subjects, of which 50 were males. None of the subjects had uterine cancer at the beginning of the study. After 40 years, 30 subjects were diagnosed with uterine cancer. No subjects were lost to follow-up. What was the incidence rate (cumulative incidence) of uterine cancer over the 40 years? Show your work.
- Is it possible to determine the prevalence of uterine cancer on the day the study ended? If yes, show your calculations. If no, explain your answer.
- Five hospital employees were prospectively followed to determine if they would get Hepatitis B after accidental needle stick exposures. One employee was followed for 1 year and he was not diagnosed with Hepatitis B. Two employees were followed for 3 years each and they were not diagnosed with Hepatitis B. One employee was diagnosed with Hepatitis B six months after the needle stick. Because he still worked in the hospital, employee health followed his medical condition closely for the next 18 months. One employee was followed for two years and she was not diagnosed with Hepatitis B. What was the incidence density of Hepatitis B in these employees? Show your work.
- A researcher wants to assess if there is an association between strokes and daily exercise in middle-aged women. She gathers 40 subjects with a stroke and 60 subjects who have not had a stroke. She then asks a series of questions and determines that 20 of the stroke subjects had hypercholesterolemia while 10 of the subjects without stroke had hypercholesterolemia. Calculate the correct measure of association between strokes and hypercholesterolemia. Show your work.
- An investigator follows 100 smokers and 200 non-smokers for 20 years. None of them had lung cancer at the start of the study. After 30 years, 15 smokers were diagnosed with lung cancer and 10 non-smokers were diagnosed with lung cancer. What is the attributable risk of cigarette smoking on lung cancer over the 20 years? Show your work.
- Surgeons are interested in the outcomes on 50 patients who had a laparoscopic colectomy between 1999 and 2001. They report that 45 patients had no complications, two had a minor post-operative infection and three patients each required a post-operative transfusion of two units of packed red blood cells. Of these 50 patients, 25 were referred to surgeons by internists and 25 were referred by family practitioners. What kind of study did the surgeons perform?
- In a retrospective cohort study, a pediatrician determines that of 50 children who did not regularly exercise, 10 were diagnosed with mild hypertension at age 22. Of 100 children who did exercise regularly, five were diagnosed with mild hypertension at age 22. Calculate a measure of association between mild hypertension at age 22 and regular exercise as a child. Show your work.
- Cardiac surgeons want to know if patients undergoing coronary artery bypass grafting (CABG) have a shorter hospital stay if they use the internal mammary artery or a leg vein for the coronary artery bypass procedure. Both are routinely used in the 550 operations per year in their hospital. What is the best study design to address this question?
Approximate Class Schedule:
|30 minutes||Instructor review of key concepts from Lectures 1, 2 and 3|
|30 minutes||Review of homework assignment|
|45 minutes||The class will be divided into small groups. Each group will critique the paper.|
|30 minutes||Class discussion on critique|
To Be Completed in Small Group Session
Answer the following questions pertaining to the paper Effects of Lifestyle Activity vs Structured Aerobic Exercise in Obese Women.
- Did the subjects likely meet entry criteria as defined by the authors? If yes, explain your answer. If not, explain your answer and indicate how this might have lead to erroneous trial conclusions.
- Were the study arms comparable? If yes, explain your answer. If not, explain your answer and indicate how this might have lead to erroneous trial conclusions.
- What was the loss to follow-up? Was it a problem?
- Was compliance properly assessed? If yes, explain your answer. If no, explain your answer and indicate how this might have lead to erroneous trial conclusions.
- Was the study double-blinded? If yes, explain your answer. If not, do you think it led to an erroneous study conclusion? Explain your answer.
- Were the outcomes, as defined by the authors, correctly assessed? Do you agree with the study’s definition of the outcomes? If yes, explain your answer. If no, indicate how this might have led to erroneous trial conclusions.
- Comment on the external validity of this paper.