NORRISK 2: A Norwegian risk model for acute cerebral stroke and myocardial infarction.

Background Guidelines for the prevention of cardiovascular disease recommend the estimation of an individual's total risk. We have developed a new model for the prediction of the 10-year risk of incident acute myocardial infarction or cerebral stroke based on Norwegian data, NORRISK 2. Design The model was based on 10-year follow-up of a large population-based cohort (CONOR) through linkage to the CVDNOR project, a database of cardiovascular disease hospital discharge diagnoses and mortality in Norway in 1994-2009. Methods We used the Fine and Gray regression model to estimate the 10-year risk adjusting for competing risk. The model population consisted of participants in 1994-1999 and the external validation population of participants in 2000-2003. We validated the model by area under the receiver operating characteristic curves, calibration plots and analyses of sensitivity and specificity. Results The model population consisted of 31,445 men and 35,267 women aged 40-79 years with 3658 endpoints in men and 2459 in women. The external validation population consisted of 19,980 men and 19,309 women, of whom 1858 men and 874 women had an endpoint during follow-up. The area under the curve was 0.79 (0.79-0.80) in men and 0.84 (0.83-0.85) in women in the model population and was slightly lower in the external validation population. Calibration plots showed good agreement between observed and predicted risk. The sum of sensitivity and specificity was greatest around the suggested risk thresholds. Conclusion The NORRISK 2 model showed good validity in an external dataset and will be a valuable tool to guide decisions about preventive interventions in people without known previous cardiovascular disease.