External validation of new risk prediction models is infrequent and reveals worse prognostic discrimination.

Siontis GC1, Tzoulaki I2, Castaldi PJ3, Ioannidis JP4.

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Abstract

OBJECTIVES:

To evaluate how often newly developed risk prediction models undergo external validation and how well they perform in such validations.

STUDY DESIGN AND SETTING:

We reviewed derivation studies of newly proposed risk models and their subsequent external validations. Study characteristics, outcome(s), and models' discriminatory performance [area under the curve, (AUC)] in derivation and validation studies were extracted. We estimated the probability of having a validation, change in discriminatory performance with more stringent external validation by overlapping or different authors compared to the derivation estimates.

RESULTS:

We evaluated 127 new prediction models. Of those, for 32 models (25%), at least an external validation study was identified; in 22 models (17%), the validation had been done by entirely different authors. The probability of having an external validation by different authors within 5 years was 16%. AUC estimates significantly decreased during external validation vs. the derivation study [median AUC change: -0.05 (P < 0.001) overall; -0.04 (P = 0.009) for validation by overlapping authors; -0.05 (P < 0.001) for validation by different authors]. On external validation, AUC decreased by at least 0.03 in 19 models and never increased by at least 0.03 (P < 0.001).

CONCLUSION:

External independent validation of predictive models in different studies is uncommon. Predictive performance may worsen substantially on external validation.

KEYWORDS:

Area under the receiver operating characteristics curve; Derivation study; Discrimination; External validation; Prognostic models; Risk prediction model