Cardiovascular risk estimation tailored to different clinical settings - the Tromso study

Objective. To develop a cardiovascular risk model simulating different clinical settings using a staged approach. Design. Using data from 27 477 men and women from the Norwegian Tromso Study in 1986-1987 and 1994-1995, Cox regression models for either myocardial infarction (MI) or stroke combined with a similar model for the competing event a risk model that assess ten-year risk of MI and stroke was developed. Explanatory variables (questions, simple examinations and blood samples) were added gradually. The model was validated using Hosmer-Lemeshow test, the Brier score, c-index, integrated discrimination improvement (IDI) and Net Reclassification Improvement (NRI). Results. In total, 1 298 events of MI and 769 events of stroke were registered. For MI the model showed excellent discrimination in each step with c-index from 0.833 to 0.946. For stroke the c-index ranged between 0.817 and 0.898. IDI showed significant increases in discrimination. The Brier scores and goodness of fit test showed well calibrated models in all steps for all sex- and end-point specific models (p>0.05). Conclusions. Although the predictive and discriminative ability of the models increased with each step, even the simplest model containing only data from questions or blood samples alone yielded valid estimates of cardiovascular risk.