Logistic Regression: A Self-learning Text, Third Edition (Statistics in the Health Sciences)

Presentation I. Overview FOCUS Assessing confounding and interaction Valid estimate of E–D relationship Three stages: (1) Variab ...

Hierarchy Principle: Significant product term ! All lower order components remain II. Interaction Assessment Stage Start with HW ...

Chunk test Not significant Eliminate all terms in chunk or Use BWE to eliminate terms from chunk Retain some terms in chunk Sign ...

Using the BWE approach, the least significant EViVjterm, sayEV 1 V 3 , is eliminated from the model first, provided it is nonsig ...

Most situations useonly EVi product terms + interaction assessment less complicated + do not needViVjterms for HWF model: To eva ...

III. Confounding and Precision Assessment When No Interaction Confounding: No statistical testing (validity issue) Confounding b ...

We refer to this estimate as thegold standard estimateof effect because we consider it the best estimate we can obtain, which co ...

In general, when no interaction, assess confounding by:  Monitoring changes in effect measure for subsets ofVs, i.e., monitor c ...

Why do not we use gold standard? Answer. Might find subset of Vs that will  gain precision (narrower CI)  without sacrificing ...

IV. Confounding Assessment with Interaction Interaction stage completed – Begin confounding Start with model containing E, all V ...

Apply hierarchy principle to identify Vi, and ViVj terms to remain in all further models Focus on Vi, and ViVj terms not identif ...

Interaction:dOR¼exp ^ bþ~^djWj  ^band^djnonzero no interaction:dOR¼expðb^Þ Coefficients change when potential confounders drop ...

The likelihood ratio test for the significance of EV 3 compares a “full” model containingE, the fourVs,EV 1 ,EV 2 ,EV 3 , andEV ...

The odds ratio that controls for all four poten- tial confounders plus retained interaction terms is given by the expression sho ...

To assess (data-based) confounding here, we must determine whether there is a meaningful difference between the gold standard an ...

Moreover, because the odds ratio expression involves the exponential of a linear function of the four coefficients, these coeffi ...

If, looking at these two tables collectively, we find thatyes, there is one or more meaningful difference in corresponding odds ...

Confounding assessment when interaction present (summary):  Compare tables of ORs and CIs  Subjective – debatable  Safest dec ...

In the variable specification stage of our strat- egy, we choose an initialE, V, Wmodel, shown here, containing the exposure var ...

A summary of the printout for the model remaining after interaction assessment is shown here. In this model, the two interaction ...