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# LectureOct8 - BME 423 Lecture Notes - Oct. 8, 2008 Methods...

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1 Methods for Proportions and Nominal Variables BME 423 Lecture Notes - Oct. 8, 2008 V. Association Between Nominal Variables A. Relative Risk B. Odds Ratio Types of Error in Inferences and Power of a Statistical Test I. The Idea II. Two Types of Errors z Test () 1 ˆˆ 11 2 ˆˆ 11 1 asp pla asp pla asp pla pp n n z n n −− + = −+ 12 ˆ mm p nn + = + == zt α ν >→ Reject H0 P < 1 n 2 n 1 m 2 m

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2 Test j ij i C ER n = ( ) 2 2 11 c r n n ij ij ij ij OE E χ == = ∑∑ ( )( ) rc vn n = −− 22 () α χν > Reject H0 P < 2 (use Yates correction only if 2x2) Quantifying the Size of a Treatment Effect – Association Between Nominal Variables Clinical Trials Patients are randomized to treatment groups and then the outcome is observed. -e.g., thrombosis development w/ aspirin vs placebo Prospectively Designed: hypothesis, # of subjects, exclusion criteria, statistical tests, etc. Clinical Trials vs Epidemiological Studies
3 Quantifying the Size of a Treatment Effect – Association Between Nominal Variables Epidemiological Studies Subjects not

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## This note was uploaded on 12/02/2008 for the course BME 423 taught by Professor D'argenio during the Fall '06 term at USC.

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LectureOct8 - BME 423 Lecture Notes - Oct. 8, 2008 Methods...

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