1 PH 241: Chapter 7 Nicholas P. Jewell University of California Berkeley February 10, 2006.

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Presentation transcript:

1 PH 241: Chapter 7 Nicholas P. Jewell University of California Berkeley February 10, 2006

2 2 x 2 Table Notation Disease Status Dnot D Exposure Eaba+b not Ecdc+d a+cb+dn

3 Cohort Study Example (Population OR = 1) Disease Status DNot D Exposure status E84250 not E Typical Study      p = 0.44

4 Cohort Study Example (Population OR = 1)  1,000 typical studies  Smallest OR estimate = 0.15  Largest OR estimate = 7.58  Average of OR estimates = 1.16 (bias)  Median of OR estimates = 1

5 Sampling Distribution of Odds Ratio Estimate not Normal--skewed

6 Cohort Study Example (Population OR = 1)  1,000 typical studies  Smallest log(OR) estimate = =log(0.15)  Largest log(OR) estimate = 2.03 = log(7.58)  Average of OR estimates = (little bias)  Median of OR estimates = 0 =log(1) I always use natural logarithms

7 Sampling Distribution of Log Odds Ratio Estimate

8 Confidence Intervals for the Odds Ratio Disease Status Dnot D Exposure Eaba+b not Ecdc+d a+cb+dn 95% CIs for log(OR) and OR

9 Case-Control Study of Pancreatic Cancer Sex Disease Status Coffee Drinking (cups/day) Total Men Case Control Women Case Control Total

10 Case-Control Study of Pancreatic Cancer Pancreatic Cancer CasesControls Coffee Drinking (cups/day)

11 Estimate & Confidence Intervals for the Relative Risk Disease Status Dnot D Exposure Eaba+b not Ecdc+d a+cb+dn 95% CIs for log(RR) and RR

12 Western Collaborative Group Study Occurrence of CHD YesNo Behavior Type Type A Type B

13 Estimate & Confidence Intervals for the Excess Risk Disease Status Dnot D Exposure Eaba+b not Ecdc+d a+cb+dn 95% CIs for ER:

14 Western Collaborative Group Study Occurrence of CHD YesNo Behavior TypeType A Type B

15 Estimate & Confidence Intervals for the Attributable Risk: Population-Based Study Disease Status Dnot D Exposure Eaba+b not Ecdc+d a+cb+dn 95% CIs for log(1-AR) and AR

16 Western Collaborative Group Study Occurrence of CHD YesNo Behavior TypeType A Type B

17 Small sample adjustments  Odds Ratio  Estimate:  CIs:  Relative Risk  Estimate:  Exact tests/CIs

18 Case-Control Study of Pancreatic Cancer Pancreatic Cancer CasesControls Coffee Drinking (cups/day) An exact 95% CI for OR is (1.64, 4.80)

19 Small Sample Ideas  Be aware when you have entered “small sample world” where approximations may not be accurate and adjustments/exact methods may be required