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# The Chi-Square Distribution and the Analysis of Frequencies (2).docx

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School
McMaster University
Department
Statistics
Course
STATS 2B03
Professor
Aaron Childs
Semester
Fall

Description
th November 6 , 2012 Stats 2B03: Statistical Methods for Science The Chi-Square Distribution and the Analysis of Frequencies (2) 12.5 Tests for Homogeneity - Example: in the physician’s health study 11,037 physicians took 325mg Aspirin, and 11,034 took a placebo every other day over a 10-year period. 104 people in the Aspirin group had a heart attack, and 189 people in the placebo group had a heart attack. We want to test H : P0=P 1 H 2 PA≠P 1 wh2re P1is the probability of a heart attack for the aspirin group, and P f2r the placebo group. Observed Table (O) Heart attack No Heart attack Total Aspirin 104 10,933 11,037 No Aspirin 189 10,845 11,034 total 293 21,778 22,071 - this is called a 2x2 contingency table - in general, we want to use the data from an r×c (rows x columns) contingency table to test:  H 0 P 1P 2…=P k  H A P≠i fsr at least one pair (i, j)  This null hypothesis is called the homogeneity hypothesi
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