Temporal Validation.
In temporal validation, the model is typically validated in more recent individuals. The purpose of such validation is to make sure that the model maintains its accuracy when it is tested in cohorts in different time periods. A model developed way back (say 20 years ago) may not work in current patients (e.g., change in risk factor distribution and availability of large dataset on many risk factors). Temporal validation can be easily achieved just splitting the data into two parts. Develop the model in one part that contains early treated patients and validate the model to assess its performance in another part that contains patients that are more recent2. Temporal validation can also be achieved through the prospective application of the developed model in specifically collected cohort2. For example, a model can be developed in a group of patients between 2005 and 2010 and the same model can be validated in a different group of patients from the same cohort between 2012 and 2015.