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

Answers about Screening (con- tinued) Q2. Yes: It depends.  Use Method 0 if severalEs andCs? No  Use Method 0 if oneEand sever ...

Question 2 (continued) What if onlyEs(noCs consid- ered)? Answer:Use Method 0. Why? Confounding not an issue Initial model withE ...

EXAMPLE Examples of Screening: SingleE,C 1 , C 2 ,...,C 10. Four Scenarios: Which of these is “legitimate”? i. Crude analyses re ...

IV. Collinearity Can someXs be predicted by other Xs? IfXs are “strongly” related, then ^bjunreliable V^ar^bjhigh model may not ...

EXAMPLE (continued) b 0 b 1 b 2 b 3 b 4 b 5 b 6 b 7 Largest CNI “large” (e.g., >30) At least two VDPs “large” (e.g., ≥ 0.5) ...

CNIs and VDPs derived fromV^ CNIs identify if collinearity exists VDPs identify variables causing collinearity SAS;STATA;SPSS do ...

We recommend (linear or logistic models):  Require CNI>> 30  Focus on VDPs for largest CNI  Address largest CNI before ...

EXAMPLE MRSA example – Initial Model: Logit PðXÞ¼aþb 1 E 1 þb 2 E 2 þg 1 V 1 þg 2 V 2 þd 11 E 1 W 1 þd 12 E 1 W 2 þd 21 E 2 W 1 ...

EXAMPLE (continued) Reduced model after diagnosing collinearity: Logit PðXÞ¼aþb 1 E 1 þb 2 E 2 þg 2 V 2 þd 12 E 1 W 2 þd 22 E 2 ...

EXAMPLE 4 predictors: E, AGE, RACE, SEX) 4 Dbvalues for each subject (i) n¼ 100 )Compute 400 Dbjvalues DbE;i;DbAGE;i;DbRACE;i;Db ...

More on influential observations including:  How to use computer software?  How to proceed when influential observations are i ...

EXAMPLE (continued) Results suggest that regression coefficients are “influenced” by these two subjects, e.g., drop subjects 9 a ...

Erroneous data + Correct if possible Drop if not correctable Correct data + Decision to delete up to researcher Report and inter ...

VI. Multiple Testing Modeling strategy)several statistical tests + Potential for incorrect “overfitted” model, i.e., “too many”s ...

Bonferroni approach: To achievea*a 0 , seta¼a 0 /T EXAMPLE e.g.,a 0 ¼0.05,T¼10: a¼0.05/10¼0.005 + a*¼ 1 (10.005)^10 ¼0.49a 0 ...

Multiple-testing literature: researcher knows in advance number of tests Modeling strategy (“best model”) problem: researcher do ...

VII. SUMMARY Five issues on model strategy guidelines: Modeling strategy when there are two or more exposure variables Screenin ...

SUMMARY (continued) Issue 3: Collinearity Diagnose using CNIs and VDPs Collinearity detected if: Largest CNI is large (>30) A ...

We suggest that you review the material cov- ered in this chapter by reading the detailed outline that follows. Then do the prac ...

Detailed Outline Abbreviated Outline I. Overview (page 244) Focus: Five issues not considered in Chaps. 6 and 7  Apply to any r ...