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From |
"Daniel, Gregory" <GDaniel@healthcore.com> |

To |
"'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu> |

Subject |
st: Date: Wed, 30 Apr 2003 15:42:26 -0400 |

Date |
Wed, 30 Apr 2003 15:42:49 -0400 (EDT) |

Dear Statalist, I am running a logistic model where I have discovered interactions between: 1) Gender [male] and Age [age_65; dichotomous]; and 2) Angioplasty [idx_angio] and Age [age_65] My confusion is in interpreting the simple effects of age at each level of the interactions. I have tried using a.age_65@g.idx_angio with i.male*i.age_65 also present in the model, but was not able to interpret the results. For example: . xi3: logistic outcome i.male*i.age_65 a.age_65@g.idx_angio i.male _Imale_0-1 (naturally coded; _Imale_0 omitted) i.age_65 _Iage_65_0-1 (naturally coded; _Iage_65_0 omitted) g.idx_angio _Iidx_angio_0-1 (naturally coded; _Iidx_angio_0 omitted) note: _Iag1Wid1 dropped due to collinearity Logistic regression Number of obs = 15877 LR chi2(5) = 403.64 Prob > chi2 = 0.0000 Log likelihood = -10093.725 Pseudo R2 = 0.0196 ---------------------------------------------------------------------------- -- Outcome | Odds Ratio Std. Err. z P>|z| [95% Conf. Interval] -------------+-------------------------------------------------------------- -- _Imale_1 | 1.312062 .0609901 5.84 0.000 1.197807 1.437215 _Iage_65_1 | 1.277411 .2022554 1.55 0.122 .9366081 1.742221 _Ima1Xag1 | .7752202 .0525718 -3.75 0.000 .6787355 .8854206 _Iidx_angi~1 | 2.334687 .2707346 7.31 0.000 1.860038 2.930459 _Iag1Wid0 | 1.603602 .249047 3.04 0.002 1.182772 2.174164 ---------------------------------------------------------------------------- -- Where _Iag1Wid1 = over65 vs. under65 at idx_angio==1; and _Iag1Wid0 = over65 vs. under65 at idx_angio==0 Why was _Iag1Wid1 dropped due to collinearity? Also is the OR for _Imale_1 (1.31) for "males versus females AT under 65 (age_65==0)"? --Or is it "males versus females AT under 65 AND no angioplasty (idx_angio==0)"? Also, I have tried the 3 way interaction: i.male*i.age_65*i.idx_angio, but none of the terms were significant. What am I missing here?? Gregory Daniel Health Core, Inc. 4735 Ogletown-Stanton Road Suite 3201 Newark, DE 19713-2094 * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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