a mortar attack ; and ( 3 ) the RO has conceded that the Veteran ' s claimed in - service stressor occurred . 38 C . F . R . § 3 . 304 ( f ) . The Board finds the evidence concerning service connection to PTSD is at least in equipoise . When there is an approximate balance of positive and negative evidence regarding any issue material to the determination of a matter , VA shall give the benefit of the doubt to the claimant . 38 U . S . C . A . § 5107 ; see also Gilbert v . Derwinski , 1 Vet . App . 49 , 53 ( 1990 ) . Accordingly , the criteria for service connection for