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Stat 100 Feb 11

Stat 100 Feb 11. Read Chapter 12, try 1-9. Problem 14 of Chapter 12. Case control study: 239 lung cancer patients and 429 controls 98 of the lung cancer patients had at some time owned a bird 101 of the controls had at some time owned a bird. Part a. Construct a contingency table.

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Stat 100 Feb 11

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  1. Stat 100 Feb 11 Read Chapter 12, try 1-9

  2. Problem 14 of Chapter 12 • Case control study: 239 lung cancer patients and 429 controls • 98 of the lung cancer patients had at some time owned a bird • 101 of the controls had at some time owned a bird.

  3. Part a • Construct a contingency table

  4. Contingency Table

  5. Contingency Table

  6. Risk of Lung Cancer • Compute the risk of lung cancer for bird owners and non-owners • Risk=percent or proportion falling into the “bad” category • For bird owners, 98/199=.492 or 49.2% • For non-owners, 141/469=.301, or 30.1%

  7. Comparing Risks • Relative Risk • Divide risk in one group by risk in other • Rel. Risk of lung cancer for bird owners= .492/.301=1.63 • Interpretation: For bird-owners, the risk of lung cancer is 1.63 times the risk for non-owners.

  8. Percent Increase in Risk • Divide difference in risks by the lower of the two risks. (express as percent) • (.492-.301)/.301=.191/.301=63% • Interpret: Having owned a bird increases the risk of lung cancer by 63%

  9. Thought Question • Do you think the risks calculated in this problem correctly describe the risk of lung cancer? • Can you think of any other explanation for the results aside from “having owned a bird increases the risk of lung cancer?”

  10. NOTE • Because this was a case-control study, cancer patients were purposely “over-sampled” • Makes risk of cancer in this sample much higher than normal risk in population

  11. Thought Question • Can you think of any other explanation for the results aside from “having owned a bird increases the risk of lung cancer?” • Maybe bird owners are more likely to smoke

  12. Odds • Comparison of chance something happens to chance it doesn’t • Suppose 42 of 92 short kids have been bullied. • Odds of being bullied are 42 to 50 • Suppose 30 of 111 normal height kids have been bullied • Odds of being bullied are 30 to 81

  13. Odds ratio • Comparison of odds for two different groups • Short kids compared to normal height – • Odds of being bullied = (42/50)/(30/81) = 2.27 • For short, odds of being bullied are 2.27 times odds for normal height

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