The committee has reviewed these goals in the light of alternatives to conducting a survey on a nationally representative sample. It judged that the informational needs of SSA regarding the size and characteristics of the population eligible for benefits, factors permitting them to work, and assessments of future changes in the prevalence of disability could not be fulfilled easily using other existing information sources.
RECOMMENDATION 3-1. The committee strongly endorses the conduct by the Social Security Administration of a well-designed, carefully pretested and statistically sound Disability Evaluation Study.
Large scale surveys like the DES are complex undertakings. They require careful planning prior to the data collection phase and refining during and after data collection. A primary principle of survey design is to determine in considerable detail what data are to be collected and how the data will be used so that decisions can be made on sample design, reliability, and collection procedures. Many federal agencies, when mounting such surveys, establish a committee of technical advisors to offer in the short-term technical input to ensure that management decisions include a careful consideration of possible alternatives. Reliance on the contractor alone to provide such input might not serve SSA well. The committee urges SSA to avail itself of such technical input in a structured manner.
In making this recommendation the committee also urges SSA to place the DES in the context of the ongoing statistical needs of the agency. For example, SSA has stated that it hopes the DES will permit better forecasting of the changes in size of the beneficiary population. This implies ongoing measurement of the size of the pool, with updated instrumentation to reflect any changes in the SSA eligibility protocol. The DES as currently designed does not provide such a capability. Thus, SSA needs to articulate, preferably before all aspects of the DES have been fixed, the methods of providing ongoing monitoring of the size of the eligible pool of beneficiaries.
The committee also believes that a detailed plan for the statistical analysis of the DES is required. This plan should include the development and validation of models that forecast the size of the disabled population and that synthesize the DES data with other data sources.
General Features of the DES Design
As originally conceived, the principal information goal of the DES was (a) to estimate the size of the population potentially eligible for disability benefits in order to assess the upper bounds for the growth of SSDI and SSI programs, and (b) to identify the factors that enable some persons with severe impairments to remain in the workforce.