This is from the Social Security Advisory Board's Aspects of Disability: Decision Making: Data and Materials. CDRs are Continuing Disability Reviews, reviews to determine whether a Social Security disability recipient is still disabled. These are required by statute. Most reviews are supposed to happen every three years. Even the most severely disabled are supposed to be reviewed every seven years (which is a waste of resources). A review by "mailer" is simply sending the disability benefits recipient a form to complete. Assuming the recipient completes the form and does not report that he or she has improved, which few do, it is almost certain that nothing will happen. Medical CDRs involve the collection of medical records to look to see how the recipient is actually doing. Note the dramatic decline in medical CDRs after George W. Bush was elected President. This was because of Social Security's severely restricted operating budget. After Democrats retook control of Congress in 2006 and Social Security's operating budget went up, the medical CDRs started going up and the nearly meaningless mailers went down, although not nearly enough to cross paths.
This chart tells the story clearly. If you want real reviews to determine whether Social Security disability recipients remain disabled, you have to appropriate sufficient operating funds. This matters greatly since CDRs save about $10.50 for every dollar spent on them.