The U.S. Social Security Administration (SSA) provides benefits to adults and children who meet the eligibility requirements for a disability as described in Title II and Title XVI of the Social Security Act. To determine whether more accurate or precise techniques exist for determining if a previously evaluated physical impairment is either more or less severe, SSA requested the National Academies assemble a committee to review new or improved diagnostic or evaluative techniques that have become generally available within the past 30 years for cardiovascular, neurological, respiratory, hematological, and digestive conditions. The resulting report presents a summary of the evidence and information around a selected subset of diagnostic and evaluative techniques.