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What is “collapsing ”? ( for epidemiologists)

What is “collapsing ”? ( for epidemiologists). Picture a 2x2 tables from Intro Epi : (This is a collapsed table; there are no strata). Odds Ratio: 2.748808 Relative Risk: 2.294118. What is “collapsing ”? ( for epidemiologists).

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What is “collapsing ”? ( for epidemiologists)

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  1. What is “collapsing”? (for epidemiologists) Picture a 2x2 tables from Intro Epi: (This is a collapsed table; there are no strata) Odds Ratio: 2.748808 Relative Risk: 2.294118

  2. What is “collapsing”? (for epidemiologists) Now add a stratifying variable which would be considered a “precision variable”: Notice the disease proportions are different across the stratifying variable, but the exposure proportions are the same. Also we have effect modification, but whatever. Unrelated. Odds Ratio: 1.324675 Relative Risk: 1.285714 Odds Ratio: 4.333333 Relative Risk: 3.0000

  3. What is “collapsing”? (for epidemiologists) If we adjust for that “precision variable,” we are creating weighted averages: Adjustment Method (Mantel Haenszel or regression) Adj. Odds Ratio: 2.809211 Adj. Relative Risk: 2.294118

  4. What is “collapsing”? (for epidemiologists) Remember originally, we had them “collapsed,” where each of the cells were just added together

  5. What is “collapsing”? (for epidemiologists) • Because there is no confounding, the RR was collapsible. The two RRs are identical! • The OR was NOT collapsible, because collapsing is a linear process (adding) on a nonlinear measure (odds) • This is the same concept as the L’Abbe plots, but in table form, rather than visual form Original Odds Ratio: 2.748808 Original Relative Risk: 2.294118 Adj. Odds Ratio: 2.809211 Adj. Relative Risk: 2.294118

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