LectureSept30

# LectureSept30 - BME 423 Lecture Notes Sept 30 2009 Methods...

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1 Methods for Proportions and Nominal Variables BME 423 Lecture Notes - Sept. 30, 2009 IV. Contingency Table A. The Idea B. Chi Squared Statistic C. Example D. More than 2x2 E. Example F. Subdividing Contingency Tables V. Association Between Nominal Variables A. Trial Types B. Relative Risk C. Odds Ratio pp. 145-158 pp. 163-170 z Statistic 32 . 0 19 6 ˆ = = asp p 72 . 0 25 18 ˆ = = pla p 55 . 0 25 19 18 6 ˆ = + + = p () 1 ˆˆ 11 2 2.33 ˆˆ 11 1 asp pla asp pla asp pla pp n n z n n −− + == −+ 0.05 2.33 ( ) 1.96 zt ν => = Reject H0 0.05 P <

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2 IV. Contingency Table Under Null Hypothesis of NO Treatment Effect: A. The Idea Under Null Hypothesis of NO Treatment Effect: 24/44 developed thrombosis (54.5% ) regardless of group 20/44 no thrombosis (45.5% ) regardless of group
3 Expected Thrombosis Formation if Aspirin has NO Effect Sample Group Developed thrombi Free of thrombi Treated Placebo (.545*25) 13.64 (.455*25) 11.36 25 Aspirin (.545*19) 10.36 (.455*19) 8.64 19 Total 24 20 44 Expected Thrombosis Formation if Aspirin has NO Effect Sample Group Developed thrombi Free of thrombi Treated Placebo (.545*25) 13.64 (.455*25) 11.36 25 Aspirin (.545*19) 10.36 (.455*19) 8.64 19 Total 24 20 44

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4 () 2 2 observed
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LectureSept30 - BME 423 Lecture Notes Sept 30 2009 Methods...

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