Hi,
I am trying to construct a logistic regression model from my data (104
patients and 25 events). I build a full model consisting of five
predictors with the use of penalization by rms package (lrm, pentrace
etc) because of events per variable issue. Then, I tried to approximate
the full model by step-down technique predicting L from all of the
componet variables using ordinary least squares (ols in rms package) as
the followings. I would like to know whether I am doing right or not.
Deleted Chi-Sq d.f. P Residual d.f. P AIC R2
stenosis 1.41 1 0.2354 1.41 1 0.2354 -0.59 0.991
x2 16.78 1 0.0000 18.19 2 0.0001 14.19 0.882
procedure 26.12 1 0.0000 44.31 3 0.0000 38.31 0.711
ClinicalScore 25.75 1 0.0000 70.06 4 0.0000 62.06 0.544
x1 83.42 1 0.0000 153.49 5 0.0000 143.49 0.000
Then, fitted an approximation to the full model using most imprtant
variable (R^2 for predictions from the reduced model against the
original Y drops below 0.95), that is, dropping "stenosis".
n Model L.R. d.f. R2 g Sigma
104.0000000 487.9006640 4.0000000 0.9908257 1.3341718 0.1192622
This approximate model had R^2 against the full model of 0.99.
Therefore, I updated the original full logistic model dropping
"stenosis" as predictor.
These two nomograms are very similar but a little bit different.
My questions are;
1. Am I doing right?
2. Which nomogram is correct
I would appreciate your help in advance.