This appendix provides information on the sources of the data, and limitations of each source. The major surveys used in this publication are:
These surveys provide the most current and comprehensive national numbers and estimates from respondent-based information. The National Organization on Disability/Louis Harris Survey was also used extensively in this publication. Estimates from surveys are within the past eight years.
The following summaries describe the surveys, their sampling formats, the size of the respondent bases, and definitions of terms used in the surveys, including how disability is measured. More details can be found in the original publications.
Survey of Income and Program Participation (SIPP)
The SIPP is a multipanel, longitudinal survey conducted by the U. S. Census Bureau. The data in this publication come from three SIPP files that are based on a number of overlapping waves and panels of the SIPP. These are:
The SIPP covers the non-institutionalized population of residents living in the United States, and collects data on source and amount of income, labor force information, program participation and eligibility data, and general demographic characteristics. The SIPP also includes disability supplements that ask questions to determine individuals' disability status. Historical background and more detailed information on the SIPP can be found on the Internet at http://www.sipp.census.gov/sipp.
Survey design and sampling. The survey design is a continuous series of national panels in which the same households are interviewed every four months for periods ranging from 2 1/2 to 4 years. A cycle of four interviews covering the entire sample and using the same questionnaire is called a wave. Interviews are conducted by personal visit and by follow-up telephone calls. All household members 15 years old and older are interviewed if possible, and proxy response is permitted when individuals are not available for interviewing.
Respondents. In the three files of data used in this publication, sample size ranged from approximately 34,000 households for file 1 to 40,000 households for files 2 and 3. A rough estimate of the number of individuals interviewed would be 85,000 to 100,000, based on an estimated average of 2.5 individuals per household.
Definitions. The questions that have been asked in the disability supplements of the SIPP were designed to be consistent with the definition of disability set forth in the Americans with Disabilities Act (ADA). People 15 years of age and older were considered to have a disability if they met the following criteria:
Functional limitations are defined from the questions asked about the difficulty in performing basic activities such as seeing, hearing, having one's speech understood, walking, carrying or lifting 10 pounds or walking up a flight of stairs. Activities of Daily Living (ADLs) covered in the survey include getting around inside the home, getting in and out of bed or a chair, bathing, dressing, eating and toileting. Instrumental Activities of Daily Living (IADLs) covered in the survey include going outside the home, keeping track of money or bills, preparing meals, doing light housework and using the telephone.
National Health Interview Survey (NHIS)
The NHIS is a principal source of information on the health of the civilian non-institutionalized population of the United States that is conducted by the National Center for Health Statistics (NCHS). Each year, the survey consists of a basic set of questions on health, socioeconomic and demographic items as well as one or more special questionnaires to obtain more detailed information on major current health issues. A Disability Follow-up special questionnaire was used in 1994-95. The NHIS also provides information about activity limitations and chronic conditions which are relevant to the topic of work and disability.
Survey Design and Sampling. The NHIS is conducted according to a multistage probability design, permitting continuous sampling of the civilian non-institutionalized population living in the United States. Each weekly sample is representative of the target population and is additive with other weekly samples. Sampling is done throughout the year, preventing seasonal bias. Information is obtained about health and other characteristics of each member of the household. The usual sample size is approximately 50,000 households.
Respondents. The interviewed sample for 1993 was 109,671 individuals and for 1994 was 116,179 individuals (45,705 households). Response rates were approximately 95.6 percent in 1993 and 94.1 percent in 1994.
Definitions. The NHIS defines chronic condition as one that has lasted for three months or more, or that is on the NCHS list of chronic conditions regardless of onset. Disability refers to the state of being limited, due to a chronic mental or physical health condition, in the type or amount of activities. The NHIS has three measures of disability: 1) limitation in major activity, 2) work limitation, and 3) need for personal assistance with activities of daily living. For working-age people, 18-69 years of age, the NHIS defines the major activity as working or keeping house.
Current Population Survey (CPS)
The CPS is a monthly survey conducted by the U.S. Census Bureau which deals mainly with labor force data for the civilian non-institutionalized population. The data presented in this publication are from the March Income Supplement, in which questions related to labor force participation and income are asked of all members of the household 16 years of age and older.
Survey Design and Sampling. The sample of approximately 60,000 is selected to be representative of the entire population of the United States, and numbers are ³weighted² or adjusted to independent population estimates based on the results of the decennial Census. These weights take into account age, gender, sex, race, Hispanic origin and state of residence.
Respondents. About 60,000 households were eligible to participate in the survey, which represents about 1 in every 1600 households in the country.
Definitions. Work disability is the only disability measured by the CPS. People are classified as having a work disability if they:
The Decennial Census ("The Census") has been conducted every 10 years since 1790. Data in this publication are based on the 1990 census. The Census seeks to simultaneously enumerate all individuals in the United States. Census forms are mailed out and interviewers dispatched to residential addresses, and the Census questionnaire includes questions about both the condition of the housing unit and its occupants.
The "short form" of the 1990 Census asked 7 population and 7 housing questions, and was intended to be completed by all households (100% sample.) The "long form" of the Census contained all of the short form questions and many other questions and was distributed to a sample of the United States population. Questions about disability are contained in the long form of the Census. Data from the decennial Census are used to weight the sample results of the SIPP and the CPS on age, sex, race, and Hispanic/non-Hispanic categories.
Survey Design and Sampling. The short form of the decennial Census, which is used to weight other surveys, does not sample from the population, but rather seeks to enumerate the entire population of the United States. About 106 million housing units received the short form. The long form of the Census, which includes disability questions, was distributed to 17.7 million housing units. The Census samples according geographical areas, and smaller, less populated areas are sampled more heavily than densely populated urban areas. The Census also conducts a Post-Enumeration Survey which is used to estimate the degree to which the Census over- or under-counts the population.
Respondents. The total population count of the 1990 Census was 247.8 million people. Researchers estimate that the Census undercounted the population by 4 - 5.3 million people, based on the results of the Post-Enumeration Survey (Hogan, 1993). The under-count is proportionally larger for certain groups of people (particularly ethnic minorities, and people with low income or low educational level) and for certain geographical areas (Barrett, 1994).
Definitions. Disability, according to the 1990 Census, is defined by answers to the following questions. The work disability question is the same as in the 1980 Census. People were asked whether they had a physical, mental or other health condition that limited the amount or kind of work they could do, prevented them from working, or prevented them from using public transportation. A question about functional disability, which was new to the 1990 Census, asked whether any person in the household had a health condition that limited his or her ability to go outside the home alone or caused difficulty in taking care of personal needs such as bathing, dressing, or getting around inside the home. (Barrett, 1994).
Annual Survey of Occupational Injuries and Illnesses (ASOII)
The Annual Survey of Occupational Injuries and Illnesses (ASOII) collects data on work-related injuries, illnesses and fatalities for the Bureau of Labor Statistics from a random sample of 165,000-280,000 private industry establishments. (Sample sizes vary from year to year.) The sample excludes employees in government agencies.
The annual survey provides estimates of the number and frequency (incidence rates) of workplace injuries and illnesses based on logs kept by private industry employers during the year. These records reflect not only the year's injury and illness experience, but also the employer's understanding of which cases are work related under current recordkeeping guidelines of the US Department of Labor. The number of injuries and illnesses reported in any given year also can be influenced by the level of economic activity, working conditions and work practices, worker experience and training and the number of hours worked.
Survey Design and Sampling. An independent sample is selected for each state. The sample design is based on the total recorded case incident rate. The sample is stratified by industry categories based on the 1987 Standard Industrial Classification (SIC) Manual.
Respondents. In 1995, the survey covered about 280,000 private establishments, representing about 83 million workers in the private sector.
National Organization on Disability (NOD) / Harris Survey on Disabilities
The National Organization on Disability (NOD) / Harris Survey on Disabilities reports on a poll commissioned by the National Organization on Disability and conducted by Louis Harris and Associates. It is the second major national survey to study the attitudes and experiences of Americans with disabilities. Using a nationwide cross-sectional sample of the population with disabilities, issues such as employment, lifestyles, political and religious participation, home computer use and the education of children with disabilities were investigated. Twenty-five minute interviews were conducted by telephone with eligible respondents. All interviews with the disabled population were conducted from February 4, 1994 to March 3, 1994. Interviews with the non-disabled population were conducted from April 4-7, 1994.
Survey Design and Sampling. Louis Harris and Associates screened more than 20,000 household randomly in the general population in order to generate a sample of 1,021 adults with disabilities aged 16 and over. The survey is based 1,021 telephone interviews. A minimum number of interviews were conducted among adults with disabilities in each of the following age groups: 16 to 24 years, 25 to 54 years and 55 years and older. This allowed the appropriate balance of interviews with working age people with disabilities. The data were then weighted to their proportions in the population. In addition, a national sample of 1,115 adults without disabilities were asked a number of the survey questions in order to provide a comparison to the non-disabled.
Respondents. All respondents in the disability sample met at least one of the definitional criteria listed below under definitions. A total of 1,021 individuals with disabilities were interviewed.
Definitions. This survey defined disability in the same fashion as the 1986 survey. A person was included in the sample of adults with disabilities if he or she: