In Barnhart v. Walton, 535 U.S. 212, 221-22, 122 S.Ct. 1265, 152 L.Ed.2d 330 (2002), the Court noted that the administrative interpretation at issue was one of longstanding duration, that Congress had frequently amended the statute in question without questioning the administrative construction, and that the statute was of sufficient complexity that it was fair to assume that Congress understood that the agency would be required to engage in policymaking when it administered the statute. See 535 U.S. at 220-22, 122 S.Ct. 1265. The Court concluded that "the interstitial nature of the legal question, the related expertise of the Agency, the importance of the question to administration of the statute, and the careful consideration the Agency has given the question over a long period of time" indicated that "Chevron provides the appropriate legal lens through which to view the legality of the Agency interpretation here at issue." Id. at 222, 122 S.Ct. 1265.