S tatistik fo r M P H : 5 F ra d en 4 . u g es statistik u n d erv isn in g : F ...
S tatistik fo r M P H : 5 F ra d en 4 . u g es statistik u n d erv isn in g : F ...
S tatistik fo r M P H : 5 F ra d en 4 . u g es statistik u n d erv isn in g : F ...
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Wh<strong>en</strong> is the st<strong>ra</strong>tified analysis s<strong>en</strong>sible?In the st<strong>ra</strong>tified analysis, we ave<strong>ra</strong>ge the <strong>in</strong>dividual OR’s from th<strong>es</strong>epa<strong>ra</strong>te st<strong>ra</strong>ta.This mak<strong>es</strong> s<strong>en</strong>se if the <strong>in</strong>dividual OR’s are roughly the same <strong>in</strong> allst<strong>ra</strong>ta (tak<strong>in</strong>g the <strong>ra</strong>ndom variation <strong>in</strong>to account).= if there is no <strong>in</strong>te<strong>ra</strong>ction betwe<strong>en</strong> exposure and st<strong>ra</strong>tificationvariable on the outcome= if there is no effect-modification of the st<strong>ra</strong>tification variable onthe relation betwe<strong>en</strong> exposure and outcome19ExampleT<strong>es</strong>ts <strong>fo</strong>r no <strong>in</strong>te<strong>ra</strong>ction existbut go beyond what we can cover <strong>in</strong> this course.Preval<strong>en</strong>ce of myocardial <strong>in</strong>farction by systolic blood pr<strong>es</strong>sure and age (Is<strong>ra</strong>eliIschemic Heart Disease Study, Kahn & Sempos, 1989).Age≥60 MI cas<strong>es</strong> MI negative TotalSBP≥ 140 9 115 124SBP< 140 6 73 79Total 15 188 203 OR=0.95Age
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