SSA administers two disability programs that provide monthly cash benefits to eligible individuals: (1) Disability Insurance (DI) for individuals (and their dependents) who have paid into the Disability Insurance Trust Fund and (2) Supplemental Security Income (SSI) for low-income individuals. To be eligible for DI or SSI benefits based on a disability, an individual must have a medically determinable physical or mental impairment that (1) prevents the individual from engaging in any substantial gainful activity and (2) is expected to result in death or has lasted or is expected to last at least 1 year. Federal law generally requires CDRs to be conducted at least once every 3 years for all DI beneficiaries whose disabilities are not considered permanent, and at intervals determined appropriate by SSA for those whose impairments are considered permanent. For SSI, federal law generally requires SSA to (1) conduct CDRs for infants during their first year of life if they are receiving SSI benefits due in part to low birth weight, and at least once every 3 years for SSI children under age 18 if their impairments are considered likely to improve, and (2) review the cases of all SSI children beginning on their 18th birthday to determine whether they are eligible for disability benefits under adult disability criteria. SSA may waive the requirement to conduct periodic legislatively- required CDRs on a state-by-state basis. SSA may also conduct CDRs that are not required by law as it deems appropriate. SSA contracts with state Disability Determination Services (DDS) agencies to initially determine whether applicants are disabled and to conduct periodic CDRs to determine whether beneficiaries continue to be disabled. DDS examiners assess whether individuals are eligible for benefits based on several criteria, including their current medical condition and ability to work. At the time beneficiaries enter the DI or SSI programs or continue their benefits following a CDR, a DDS examiner determines beneficiaries’ due dates for a subsequent CDR based on their potential for medical improvement. Beneficiaries classified as “medical improvement expected” are generally scheduled for a CDR within 6 to 18 months, beneficiaries classified as “medical improvement possible” are scheduled once every 3 years, and beneficiaries classified as “medical improvement not expected” are scheduled once every 5 to 7 years. To cost-effectively manage its CDR workload, SSA conducts CDRs in different ways. In general, beneficiaries with a high likelihood of medical improvement are referred for a full medical review—an in-depth assessment of a beneficiary’s medical and vocational status. Beneficiaries with a low likelihood of medical improvement are, at least initially, sent a questionnaire known as a mailer. If beneficiaries respond to a mailer in certain ways, SSA may refer these individuals for a full medical review. In contrast to mailers, full medical reviews are more labor intensive and expensive. Full medical reviews result in a decision to either cease or continue an individual’s benefits. In fiscal year 2013, the cessation rate for CDRs involving full medical reviews was about 19 percent, whereas the cessation rate for all CDRs including mailers was about 5 percent. Each year, SSA allocates a portion of its program integrity budget to CDRs, which affects the number of full medical reviews and mailers that the agency initiates during the year. When the number of cases due for a CDR exceeds SSA’s capacity to conduct full medical reviews and mailers, the cases not initiated during the year are considered backlogged for future review. The number of CDRs completed as full medical reviews, as mailers only, or backlogged varied during fiscal years 2003 through 2013 (see fig. 1). After the authority for special funding to process CDRs expired in fiscal year 2002, backlogged CDRs increased from about 100,000 cases in fiscal year 2003 to more than 1 million in fiscal year 2007, reaching a peak of nearly 1.5 million in fiscal year 2009. At the same time, the number of full medical reviews fell from nearly 670,000 in fiscal year 2003 to less than 190,000 in fiscal year 2007 before rebounding to nearly 429,000 in fiscal year 2013. SSA estimates the accuracy rate of CDRs and separately estimates the cost savings that result from CDRs. In addition to annually reporting the nationwide accuracy rate of all CDRs to the Congress, SSA internally tracks CDR accuracy rates by state and generates estimates for the accuracy of cessations and continuances, separately as well as combined. For fiscal year 2013, SSA reported an accuracy rate of 97.2 percent for CDR decisions. For the same year, SSA reported an estimated ratio of federal program savings to costs for performing CDRs as $15 to $1. Savings from CDRs include federal benefits that would be paid to individuals were it not for a CDR that resulted in a cessation. Such benefits include those from Medicare and Medicaid because in certain situations individuals’ eligibility for DI or SSI confers eligibility for these other programs. Because SSA does not complete all CDRs as scheduled due to competing priorities and existing resources, the agency must decide which cases will receive a full medical review. SSA uses a range of inputs to prioritize which CDRs to conduct, such as: Statutory requirements: Legal requirements to review SSI children beginning at age 18 to determine if they are eligible for benefits under adult disability criteria, and reviews of children up to 1 year old who are receiving SSI benefits due in part to low birth weight. SSA policies: Rules established by SSA to guide prioritization. For example, SSA prioritizes cases with particular responses to its mailers and cases with a “medical improvement expected” designation that are coming up for review for the first time. Statistical models: A set of statistical models that score each case according to the likelihood of medical improvement, typically the sole criterion for ceasing benefits. SSA’s prioritization process determines which CDRs are initiated and in what form: full medical review or mailer. To begin, SSA initiates full medical reviews of cases that fall into two high-priority categories: first, statutory requirements, and then SSA policies. Once full medical reviews of all high-priority cases are initiated, SSA prioritizes the remaining cases by using its statistical models. Full medical reviews of cases with the highest scores (i.e., highest likelihood of medical improvement) are initiated as resources permit, first by beneficiary group (i.e., DI, SSI children, SSI adults) and then by the statistical scores of cases within the group (see fig. 2). Cases with lower scores (i.e., lower likelihood of medical improvement) receive a mailer or are backlogged for future review. The extent to which the statistical models have been used to select cases for full medical reviews has varied by year, but the models have been consistently used for determining who receives mailers. Specifically, we found that the extent to which SSA’s statistical models were used to select cases for full medical review was related to the combination of budget fluctuations for CDRs, SSA’s statutory requirements, and agency policies. We estimate that the statistical models were the basis for selecting 11 to 60 percent of full medical reviews completed annually in fiscal years 2003 through 2013 (see fig. 3). In contrast, SSA has used the models consistently since 1993 to determine which cases should receive a mailer. Although SSA annually assesses its models’ performance, the agency has not updated the models since 2007. The models’ effectiveness depends on their ability to accurately predict beneficiaries’ likelihood of medical improvement. To test the accuracy of the models, SSA conducts an annual validation process using a sample of completed cases to evaluate how well the models predicted medical improvement. According to SSA officials, the model validation process has shown that the models’ accuracy in predicting medical improvement has not degraded substantially in recent years. In addition to model validation, in the past SSA has conducted periodic re-estimation of its statistical models to help ensure that they are up-to- date. In re-estimating its models, SSA updates the relationship between existing variables and medical improvement and tests whether new variables should be included. Re-estimation is particularly important when advances in medicine and assistive technology affect people’s ability to work. In recent years, SSA has changed its classification of certain beneficiaries’ impairments to reflect advances in medical knowledge. For example, in 2015, SSA revised its codes for cancer in light of new diagnoses and treatments. Because these codes can appear as variables in the statistical models, it is possible that the models are no longer accurately capturing the effect of cancer-related impairments on the likelihood of medical improvement. Although SSA officials believe that some advances would not markedly affect the accuracy of the models, the agency has not completed a re-estimation to confirm the effect of such changes. In addition, demographic changes in the underlying population of disability beneficiaries, which has grown substantially in recent years due in part to baby boomers reaching their disability-prone years, could also affect the accuracy of the models. The contractor that SSA hired to handle its last model re-estimation in 2007 provided SSA with a set of programs that would allow the agency to re-estimate the models in-house. Regular re-estimation and updating of predictive models is a best practice, and the contractor anticipated that SSA would do so at least every 3 years. Model accuracy leads to savings for SSA in two ways. First, model accuracy is important for identifying cases that are unlikely to result in medical improvement and can therefore be handled as mailers. According to SSA’s contractor, the models’ last re-estimation in 2007 increased the accuracy of the models while allowing SSA to process over 25,000 additional cases as mailers, potentially saving the agency over $20 million by performing fewer full medical reviews.