1. Transferability/generalizability deserves more attention in 'retest' studies in diagnosis and prognosis;Tugwell;J Clin Epidemiol,2015
2. Clinical prediction models are not being validated;Tugwell;J Clin Epidemiol,2015
3. External validation of new risk prediction models is infrequent and reveals worse prognostic discrimination;Siontis;J Clin Epidemiol,2015
4. External validation is only needed when prediction models are worth it;Martens;J Clin Epidemiol,2015
5. Response to letter: more rigorous, not less, external validation is needed;Siontis;J Clin Epidemiol,2015