When applying for Social Security disability (SSD) benefits, you need to demonstrate to its disability examiners that you suffer from an impairment that prevents your working and earning a living. You have to show that this impairment has lasted at least twelve months, is expected to continue for that period or will lead to your death.
This impairment must be shown by medical evidence, like that from a medical test, a series of treatments, or a diagnosis of a severe medical impairment, such as damage to your spine, lung cancer or severe heart disease. SSA makes the determination, not the doctor, so a doctor stating you are "disabled" only provides "some evidence" that you have a potentially disabling condition.
The process also involves an assessment of whether you are able to work in any occupation. This is important and is often the device by which SSA will deny an application. This process has been recently criticized by some federal appellate judges in Seventh Circuit.
Judge Posner has been very sharp in his criticism of SSA's occupational experts and the Dictionary of Occupational Titles, which was last updated in 1991 and contains numerous occupations that no longer exist while lacking jobs that have been created in the intervening 25 years.
In one opinion, Judge Posner notes that particular jobs identified by SSA's vocational expert seemed either beyond the capabilities of the applicant or were unlikely to exist at all and that statistical evidence described by the expert was likely an outright "fabrication."
The Dictionary of Occupational Titles is in the process of being replaced but it may be 2019 before that process is complete. Given the judge's skepticism toward the validity of vocational testimony, you would think that SSA would be more careful and circumspect in its claims during appeals, but the agency appears to still rely heavily on this information.
Source: theindianalawyer.com, "Disability denials draw criticism," Marilyn Odendahl, April 6, 2016