active military service beyond the condition ' s natural progression ? Any clear and unmistakable ( obvious , manifest , or undebatable ) evidence which serves as the basis for any opinion must be specifically identified . ( e ) If a current psychiatric disorder was not present during service then is it at least as likely as not ( 50 percent or greater probability ) that the current psychiatric disorder is otherwise etiologically related to the Veteran ' s period of active service ? ( f ) Do the diagnosed psychiatric disorders , including PTSD , prevent the Veteran from securing or following a substantially gainful occupation ? The opinions provided must specifically reflect consideration of the Veteran ' s military performance evaluations and his post service