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HW_2_Solution

HW_2_Solution - Homework#2 Solution 1 pts BME 423 Fall 2008...

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Homework #2 Solution BME 423 Fall 2008 1. ( pts) Null hypothesis: There is no statistically significant association between traveling abroad and being positive for P. alcalifaciens among people with gastroenteritis. Observed results: P. alcalifaciens Recent travel abroad? positive negative Total Surgical 25 229 254 Medical 5 368 373 Total 30 597 627 Expected contingency table if there is no difference between the travel abroad and not travel abroad: P. alcalifaciens Recent travel abroad? positive negative Total Surgical 12.15 241.85 254 Medical 17.85 355.15 373 Total 30 597 627 2 2 ( observed-expected 0.5) expected χ = 2 2 2 2 ( 25 12.15 0.5) ( 229 241.85 0.5) ( 5 17.85 0.5) ( 368 355.15 0.5) 12.15 241.85 17.85 355.15 χ = + + + 2 2 22.158 χ = (2 1) (2 1) 1 ν = × = 2 2 0.05 22.158 (1) 3.841 χ χ = > = 2 2 0.001 22.158 (1) 10.828 χ χ = > = Conclusion: Reject null hypothesis. There is a statistically significant association between traveling abroad and being positive for P. alcalifaciens among people with gastroenteritis (p<0.001).
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2. ( pts) Null hypothesis: There is no statistically significant association between traveling abroad and
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