38 U.S.C. § 5107

(a) Claimant Responsibility .— Except as otherwise provided by law, a claimant has the responsibility to present and support a claim for benefits under laws administered by the Secretary. (b) Benefit of the Doubt .— The Secretary shall consider all information and lay and medical evidence of record in a case before the Secretary with respect to benefits under laws administered by the Secretary. When there is an approximate balance of positive and negative evidence regarding any issue material to the determination of a matter, the Secretary shall give the benefit of the doubt to the claimant.