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This discussion is meant to help users who are beginning to use disability statistics or who want a clearer understanding of data sources.
The most often-used sources of disability statistics in the U.S. are those based on large-scale surveys conducted by the federal government. These surveys are intended to help guide policy decisions of various federal agencies. They also offer researchers, advocates, local policy-makers, and others valuable data they can use to identify needs, create programs to meet those needs, and shape proposals for improving policies.
One advantage of these large scale federal surveys is their reliability, since they are nationally representative and involve relatively large samples of households or individuals. Another advantage is the availability of the data they yield. All the major surveys done by the federal government maintain their own Web sites, providing information for a wide range of users. Typically, this includes data summaries, descriptions of the survey design and content, explanation of the sampling and weighting strategies used, the survey instruments themselves, publications, and availability of micro-level data.
Nearly all federally-sponsored surveys that deal with disability-relevant data allow users to download data sets directly from the surveys' Web sites. Surveys usually also make these data sets available on CD-ROM as well.
Some Web sites, such as the U.S. Census and the Behavioral Risk Factor Surveillance System, provide aggregate data in the form of prepared charts and summary tables. They also allow users to specify the geographic, demographic, and other variables of interest.
Depending on the user's information needs and skill in doing statistical analysis, either aggregate data or analysis of micro-level data may be more appropriate.
Micro-level data sets include data on each individual or household surveyed, with codes (usually numbers) representing the response for each question the person is asked. The set of all responses for an individual is called a record. Some records represent answers that a person gives about himself or herself; others represent answers that the person gives about other members of the household. Each of these records has an identifier that allows a researcher to retrieve a particular record or set of records. Micro-level data sets may contain tens of thousands of records.
Users familiar with statistical software such as SPSS, Stata, or SAS can conduct a variety of statistical analyses on specified variables for all records or a subset of records in the data set. The advantage of using micro-level data is that users can develop customized analyses using specified variables of interest.
Aggregate data are summary-level data, the result of applying statistical analyses to micro-level data sets. Analysis may entail summing the number of each type of response for a given variable, then applying additional calculations such as weighting and estimation of sampling error. These procedures are meant to provide reliable inferences about an entire population based on data collected from the sample, or set of samples, surveyed.
Aggregate data provide estimates of selected characteristics of the entire population surveyed (for example, how many people in the U.S. have a disability) or a specific sub-set of the population (for example, the proportion of working-age women with disabilities who have college degrees). Aggregate data are frequently used to describe trends over specific time periods (for example, how the employment rate for people with disabilities has changed from year to year since 1994).
As noted earlier, the Web sites of many federally sponsored surveys provide aggregate data on their Web sites in the form of tables, graphs, or maps. One limitation of these prepared aggregate data is that they might not use all the variables of interest to the user.
Major statistical data sources on disability
•Decennial Census and Supplementary Surveys
•American Community Survey
•Survey of Income and Program Participation (SIPP)
•Current Population Survey (CPS)
•National Health Interview Survey (NHIS)
•National Health Interview Survey on Disability (NHIS-D)
•Behavioral Risk Factor Surveillance System (BRFSS)
•Medical Expenditure Panel Survey (MEPS)
•N.O.D./Harris Survey of Americans with Disabilities
United Nations Statistics Division - Disability Statistics
This site provides a statistical reference and guide to national
sources of disability, basic disability prevalence rates, and questions
used in each national survey to identify persons with disabilities. The
data available on this site are in the United Nations Disability
Statistics Database, version 2 (DISTAT-2).
World Health Organization - International Classification of Functioning, Disability, and Health.
This site does not include disability data, but provides extensive
information on WHO's current system for classifying disability. The
system is noteworthy for its recognition of disability as an
interactional process between the person and his or her environment.