For each epoch, this variable should be derived as cvd.ever.factor="Yes" if the current or previous epoch has cvd.factor="Yes". In addition, we can check whether cvd.factor variable is monotonically coded. That is to say, if epoch 1 cvd.factor="Yes", then all the subsequent epoch shold have cvd.factor="Yes".
For each epoch, this variable should be derived as cvd.ever.factor="Yes" if the current or previous epoch has cvd.factor="Yes". In addition, we can check whether cvd.factor variable is monotonically coded. That is to say, if epoch 1 cvd.factor="Yes", then all the subsequent epoch shold have cvd.factor="Yes".