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Lecture 8

Lecture 8 notes (november 1)

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Larry Sawchuk

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November 1 Lecture: Kahn, H Intro to epidemiologic methods 1985  readings for today’s class 3 assignment: - Going to make challenging part a bonus st Nov 1 : Formula and source: OR calculator (Refer to PowerPoint slides posted oct 30 “complications…”) Slide 1: A + B  C A= risk factor or exposure factor Confounding or effect modification Confounding: Is something you want to avoid Effect modification: Is a little more informative, we can conceive of this as saying there is a relationship between a and b Categories such as age groups are what we refer to as strata or levels. Relationship of a and b changes depending on which level or strata you are operating on. i.e smoking when you are 50 as opposed to being 15. Slide 2: Effect modification is : Are the 3 strata homogeneous? Is the effect the same? If we compute an OR for one strata is it 1? How about for the next strata? Strata could be age (physiological), sociological, you can have different strata with different ethnicities (can be testing intrinsically genetics or diets) Effect modification is a really good tool to see if the relationship between a and be stay constant. Slide 3: Assess interactions mathematically Slide 4: i.e. primary risk factor for having a heart attack is hypertension Effect modification then is AGE Slide 5: Ordinary chi square/ complicate chi square Null hyp: no association between blood pressure and heart attack Alternative: there is Slide 6: Contingency chi square does not depend on sample size MH chi square: Only 2 by 2 Slide 7: Screw this table it is wrong Slide 8: 1 degree of freedom 3.84= critical value We can conclude that age and heart attacks are associated. They are interrelated. OR value: 3.44 4>1.67 therefore there is signifcantly more people having heart attacks. Slide 9: Adjusted residuals: statistical way to figure out whether or not that cell is statistically significant. If adj residual > 1.67 ; there are significantly more… than expected than chance. <1,67 tells us there are significantly less than expected. Slide 10: This is the proper way of stating odds ratio. This is the template for OR value statement (assignment 3). Slide 11: Proper values will be given next week. Slide 12: OR>1, then there is an association Chi square is
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