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. Author manuscript; available in PMC: 2017 Aug 1.
Published in final edited form as: Ann Surg Oncol. 2016 Jan 28;23(8):2471–2479. doi: 10.1245/s10434-015-5083-1

Table 3.

Comparison of Model Fit, Calibration, and Discrimination of Multivariable Logistic Regression Model of Risk Factors for Surgical Site Infection (SSI) After Mastectomy, Derivation (2004–2008) Versus Validation Cohort (2009–2011)

Derivation Cohorta Validation Cohort –
Fit Using Parameter
Estimates From
Derivation Modelb 		Validation Cohort –
Refitting Model
With Variables
From Derivation
Modelc
Hosmer-Lemeshow P 0.091 0.462 0.635
C-statistic 0.657 0.649 0.669
Brier score 0.074 0.087 0.086
a

The derivation model was also fit with a more restricted set of variables (obesity, diabetes, smoking-related diseases, bilateral mastectomy, implant reconstruction, and flap reconstruction) to determine the impact of the additional conditions on model performance. The derivation model fit with the more restricted set of variables had a significantly lower C-statistic (0.637) compared to the full model above (P = 0.007),37 Hosmer-Lemeshow P = 0.775, and Brier score = 0.075.

b

The validation model was fit using the beta coefficients of all variables in the final derivation cohort model.

c

Model used the variables from the final derivation cohort model, re-fit in the validation cohort (i.e., parameter estimates allowed to vary compared to the derivation model).