What is considered disabled for purposes of disability benefits?

An individual is considered disabled for purposes of disability benefits if he is unable to engage in any substantial, gainful activity by reason of any medically determinable physical or mental impairment that can be expected to result in death or that has lasted, or can be expected to last, for a continuous period of not less than twelve months. 42 U.S.C. 423(d)(1)(A), 1382c(a)(3)(A); see also Barnhart v. Thomas, 540 U.S. 20, 23 (2003). The impairment or impairments must result from anatomical, physiological, or psychological abnormalities that are demonstrable by medically accepted clinical and laboratory diagnostic techniques and must be of such severity that the claimant is not only unable to do his previous work, but cannot, considering his age, education, and work experience, engage in any other kind of substantial, gainful work that exists in the national economy. 42 U.S.C. 423(d)(2)-(3), 1382c(a)(3)(B), (D).