LectureSept28

# LectureSept28 - BME 423 Lecture Notes Sept 28 2009 Methods...

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1 Methods for Proportions and Nominal Variables BME 423 Lecture Notes - Sept. 28, 2009 I. Nominal (Categorical) Data A. The Population B. Estimating Proportions from Samples II. Hypothesis Tests for Proportions A. z Test B. Yates Correction III. Examples A. Halothane vs Morphine B. Aspirin vs Placebo Categorical Data Comprise Much of Clinical Research A. Nominal – (e.g, Good Outcome: Y or N) B. Ordered – (e.g., pain score: none, mild, moderate, severe) Can Describe Events Involving Categorical Data by Counting and Calculating Proportions Example: Halothane vs Morphine in Heart Surgery Lived Died Total Halothane 53 8 61 Morphine 57 10 67 Is this difference due to a clinical effect or random sampling?

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2 A. The Population M=50 N-M=150 N=200 prop. left = prop. right = M p N 1 NM p N ≡− Given RV X (e.g, left-footedness; positive test result) x=1 (have attribute) M x=0 (don’t have attribute) N-M In General Mean of X () 1 ,1 , , 11 (1) ( ) (0) i N i i xi N M xMN M NN N μ = = == + −= ii Population Proportion M p N = x f(x) 0 1 M/N (N-M)/N
3 Variance of X () 2 22

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LectureSept28 - BME 423 Lecture Notes Sept 28 2009 Methods...

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