Selection Bias

1. RR = 7 Selection Bias Is the association causal? Selection Bias Detectives in the Classroom - Investigation 3-6: Selection Bias

2. Hypotheses 1 How is this disease distributed? 2 Is there an association? 4 What should be done to prevent the disease? 5 Did the prevention strategy work? Where are we and where are we going? What’s my hypothesis? Did the exposure and the disease turn up together? 3 Is the association causal? Why did the exposure and the disease turn up together? Detectives in the Classroom – Investigation 3-6: Selection Bias

3. Investigation 3-6 1. Cause 2. Chance 3. Confounding Reversed Time Order 4. 5. Selection Bias Detectives in the Classroom - Investigation 3-6: Selection Bias

4. Explanations for Finding an Association Bias Detectives in the Classroom - Investigation 3-6: Selection Bias

5. Epi Talk Epi Talk Bias A faulty assumption in a study that makes things appear differently from how they really are. Detectives in the Classroom - Investigation 3-6: Selection Bias

6. Explanations for Finding an Association Selection Detectives in the Classroom - Investigation 3-6: Selection Bias

7. Epi Talk Epi Talk Selection Bias A faulty assumption in a study because of a systematic difference in how subjects were chosen to be in the study. Detectives in the Classroom - Investigation 3-6: Selection Bias

8. No Outcome Outcome Exposure No Exposure Association Relative Risk Risks 50 % or a b 10 c d 5 % or Detectives in the Classroom - Investigation 3-6: Selection Bias

9. Study finds …. Study Finds Association Between Heavy Backpacks and Back Pain Martin Luther King High School Heavy Backpack = 15% or more of body weight 200 students Detectives in the Classroom - Investigation 3-6: Selection Bias

10. 1 Epi Log Worksheet Detectives in the Classroom - Investigation 3-6: Selection Bias

11. Epi Teams Detectives in the Classroom - Investigation 3-6: Selection Bias

12. - Time Cross-Sectional Study E E DZ DZ Detectives in the Classroom - Investigation 3-6: Selection Bias

13. Investigators found …. Study Finds Association Between Heavy Backpacks and Back Pain 20 heavy backpacks 10 students with back pain 180 no heavy backpacks 30 students with back pain Detectives in the Classroom - Investigation 3-6: Selection Bias

14. 2 Epi Log Worksheet Detectives in the Classroom - Investigation 3-6: Selection Bias

15. Study finds …. Study Finds Association Between Heavy Backpacks and Back Pain 20 heavy backpacks 10 students with back pain 180 no heavy backpacks 30 students with back pain Detectives in the Classroom - Investigation 3-6: Selection Bias

16. Back Pain No Back Pain 10 Heavy Backpacks 50 10 10 20 20 2.9 30 No Heavy Backpacks 16.7 30 150 180 180 X 2.9 Epi Log Worksheet Detectives in the Classroom - Investigation 3-6: Selection Bias

17. Selection Bias Detectives in the Classroom - Investigation 3-6: Selection Bias

18. Selection Bias Detectives in the Classroom - Investigation 3-6: Selection Bias

19. Back Pain No Back Pain 10 Heavy Backpacks 50 10 10 20 20 2.9 30 No Heavy Backpacks 16.7 30 150 180 180 X 2.9 Selection Bias Detectives in the Classroom - Investigation 3-6: Selection Bias

20. Selection Bias Selection Bias A faulty assumption that occurs because there are systematic differences in characteristics between those who are selected for study and those who are not. Detectives in the Classroom - Investigation 3-6: Selection Bias

21. RR = 7 Explanations for Finding an Association Could the association have been found because of selection bias? Detectives in the Classroom - Investigation 3-6: Selection Bias

22. Study Links Eating M&M’s To Decreased Risk of Flu Explanations for Finding an Association Cause 1. 2. 3. 4. Chance Confounding Reversed Time Order Why would an exposure and an outcome turn up together? 5. Selection Bias Detectives in the Classroom - Investigation 3-6: Selection Bias

23. Investigation 3-6 has ended. CDC Selection Bias Detectives in the Classroom - Investigation 3-6: Selection Bias