title: Validation of a melanoma prognostic model.
abstract: BACKGROUND
  A "clinically accessible," 4-variable (patient age, patient sex, tumor location, and tumour thickness) prognostic model has been published previously. This model evaluated variables that were commonly available to the clinician. Because models are heuristic, validity of a prognostic model should be evaluated in a population different from the original population.
  
  
  OBJECTIVE
  To evaluate the external validity of this 4-variable melanoma prognostic model.
  
  
  METHODS
  To estimate the external validity of this model, we used a population-based cohort of individuals with melanoma. We also evaluated a 1-variable model (tumor thickness). Estimates of the external validity of these logistic regression models were made using the c statistic and the Brier score.
  
  
  METHODS
  A total of 1261 patients with melanoma evaluated in a multispecialty, university-based practice and 650 patients with melanoma from throughout Connecticut.
  
  
  METHODS
  Death from melanoma within 5 years of diagnosis.
  
  
  RESULTS
  The c statistics for the 4-variable model were 0.86 (95% confidence interval [CI], 0.83-0.89) for the university-based practice data set and 0.81 (95% CI, 0.75-0.86) for the Connecticut data set. For thickness alone, the c statistics were 0.83 (95% CI, 0.80-0.86) and 0.79 (95% CI, 0.74-0.85), respectively. Brier scores for the 4-variable model were 0.09 (95% CI, 0.08-0.10) and 0.08 (95% CI, 0.06-0.09) and for the 1-variable model were 0.09 (95% CI, 0.08-0.10) and 0.08 (95% CI, 0.07-0.10), respectively. No significant differences exist between the data sets for the 4- and 1-variable models.
  
  
  CONCLUSIONS
  The 4- and 1-variable models are generalizable. The simpler 1-variable model--tumor thickness--can be used with a relatively small loss in accuracy.
authors.affiliation: Department of Dermatology, University of Pennsylvania School of Medicine, Philadelphia, USA. Margolis@cceb.med.upenn.edu
authors.forename: D J
authors.initials: DJ
authors.lastname: Margolis
authors.forename: A C
authors.initials: AC
authors.lastname: Halpern
authors.forename: T
authors.initials: T
authors.lastname: Rebbeck
authors.forename: L
authors.initials: L
authors.lastname: Schuchter
authors.forename: R L
authors.initials: RL
authors.lastname: Barnhill
authors.forename: J
authors.initials: J
authors.lastname: Fine
authors.forename: M
authors.initials: M
authors.lastname: Berwick
mesh_terms: D005260:Female; D006801:Humans; D008297:Male; D008545:Melanoma / Q000401:mortality*; D008875:Middle Aged; D015233:Models, Statistical; D011379:Prognosis; D012878:Skin Neoplasms / Q000401:mortality*