When adjudicating a claim for veterans benefits, "[t]he Secretary shall consider all information and lay and medical evidence of record." 38 U.S.C. § 5107(b). Lay evidence may be competent to prove the existence of a chronic disease that can be diagnosed or demonstrated without medical expertise in presumptive service-connection claims. See Savage v. Gober, 10 Vet. App. 488, 495 (1997) (for certain chronic diseases, lay evidence may be competent to identify in-service existence of chronic disease and whether current condition is subsequent manifestation of that same chronic disease); 38 C.F.R. §§ 3.303(b), 3.307(a), 3.309(a). The distinction between the use of lay evidence in direct service-connection claims and presumptive service-connection claims for chronic diseases exists because in the latter case the lay evidence is not being used to establish a medical causation or etiology but rather to establish, by evidence of observable symptomatology, that the currently diagnosed chronic disease is the same condition that was present during service or during the presumptive period of § 3.307(a).
In its role as factfinder, the Board must first "determin[e] whether lay evidence is credible in and of itself, i.e., because of possible bias, conflicting statements, etc." Buchanan v. Nicholson, 451 F.3d 1331, 1334-37 (Fed. Cir. 2006); see also Miller v. Derwinski, 3 Vet. App. 201, 204 (1992). In certain situations, lay evidence may be used to diagnose a veteran's medical condition. See Jandreau v. Nicholson, 492 F.3d 1372, 1377 (2007) (holding that lay evidence may be used to diagnose a condition when "(1) a layperson is competent to identify the medical condition, (2) the layperson is reporting a contemporaneous medical diagnosis, or (3) lay testimony describing symptoms at the time supports a later diagnosis by a medical professional"); Barr v. Nicholson, 21 Vet. App. 303, 307 (2007) (stating that "[l]ay testimony is competent ... to establish the presence of observable symptomatology and 'may provide sufficient support for a claim of service connection' " (quoting Layno v. Brown, 6 Vet. App. 465, 469 (1994))); Washington v. Nicholson, 21 Vet. App. 191, 195 (2007) (holding that, "[a]s a layperson, an appellant is competent to provide information regarding visible, or otherwise observable, symptoms of disability").
Further, lay evidence may be competent to show continuity of symptomatology under 38 C.F.R. § 3.303(b). See Davidson v. Shinseki, 581 F.3d 1313, 1315-16 (Fed. Cir. 2009) (rejecting the view that "competent medical evidence is required ... [when] the determinative issue involves either medical etiology or a medical diagnosis." (citing Jandreau, 492 F.3d at 1376-77)); Savage v. Gober, 10 Vet. App. 488, 497 (1997). When considering lay evidence, the Board should determine whether the veteran's disability is the type of disability for which lay evidence is competent. See Jandreau, 492 F.3d at 1377. If the disability is of the type for which lay evidence is competent, the Board must weigh that evidence against the other evidence of record in making its determination regarding the existence of a service connection. Buchanan, 451 F.3d at 1334-37.
The Board "cannot determine that lay evidence lacks credibility merely because it is unaccompanied by contemporaneous medical evidence." Buchanan, 451 F.3d at 1337. Section 3.307(b) does not require both medical and competent lay evidence to establish the existence of a chronic disease, and thus, "competent lay evidence can be sufficient in and of itself" to establish entitlement to a benefit. Buchanan, 451 F.3d at 1335 (citing 38 C.F.R. § 3.307(b) (in claiming chronic disease, "factual basis may be established by medical evidence, competent lay evidence[,] or both.")).