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Unformatted text preview: ate the expected cell counts and then use the CHITEST worksheet formula. This gives the P‐value but not the test statistic itself. You can of course program the spreadsheet to find the value of Χ2. The Excel output shows the observed and expected cell counts and the P‐value. If the chi‐square test is significant, it is important to look at the data to learn the nature of the relationship. We have three ways to look at the quality‐of‐life data: • Compare appropriate percents: which outcomes occur in quite different percents of Canadian and American patients? This is the method we learned in chapter 6. • Compare observed and expected cell counts: which cells have more or fewer observations than we would expect if H0 were true? • Look at the terms of the chisquare statistic: which cells contribute the most to the value of Χ2? Example (23.4) Canada and the United States: Conclusions There is a significant difference between the distributions of quality of life reported by Canadian and American patients a year after a heart attack. All three ways of comparing the distributions agree that the main difference is that a higher proportion of Canadians report that their quality of life is worse than before their heart attack. Other response variables measured in the study agree with this conclusion. The broader conclusion, however, is controversial. Americans are likely to point to the better outcomes produced by their much more intensive treatment. Canadians reply that the American advantage comes at high cost. The resources spent on expensive treatment of heart attack...
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- Spring '08