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Recently, the Northeast ADA Center received an email that asked for direction in understanding estimates of the numbers and percentage of people with disabilities in the United States. The emailer was looking at the American Community Survey (ACS) estimates of 12.7% (2017, 1-yr estimates). They had heard that the percentage of the population with a disability was more like 20% or even higher, but they were struggling to locate the data sources and methods used to calculate those higher percentages.

Disability prevalence rates can be quite confusing; after more than 15 years of working with disabilities statistics, I’m still learning the ins and outs of it! Different data sources often use different definitions and questions to define disability. Even surveys that use the same questions to identify disability can result in different estimates. Some of this variation might be due to differences in sampling and/or methodology (in-person interview, phone based, paper based, etc.). Another major factor appears to be the content and context of the survey—prevalence rates tend to be higher in a health focused survey than in a survey focused on employment and income.

Even the position of the disability questions within the survey may have an impact. If questions about disability are presented after questions on health insurance, respondents may be “primed” to be thinking about their health when answering the disability questions. The individual may be more likely to respond “yes” to a disability item.

So where does the 20% figure come from? That number comes from a report: Americans with Disabilities: 2010, based on Census Bureau analysis of the Survey on Income and Program Participation (SIPP). It estimated that in the United States there were 56.7 million persons with disabilities, for a prevalence rate of 18.7%. How can it be that much higher? In large part it is due to the SIPP’s broad “kitchen sink” definition of disability, which includes over 100 questions about specific functional and participatory activities, health conditions, and symptoms. In comparison the ACS uses a much more basic six disability question sequence that doesn’t provide the full coverage of what disability is that the SIPP’s 100+ questions can. Below are the six ACS disability categories with the actual questions used:

• Hearing Disability (asked of all ages): Is this person deaf or does he/she have serious difficulty hearing?
• Visual Disability (asked of all ages): Is this person blind or does he/she have serious difficulty seeing even when wearing glasses?
• Cognitive Disability (asked of persons ages 5 or older): Because of a physical, mental, or emotional condition, does this person have serious difficulty concentrating, remembering, or making decisions?
• Ambulatory Disability (asked of persons ages 5 or older): Does this person have serious difficulty walking or climbing stairs?
• Self-Care Disability (asked of persons ages 5 or older): Does this person have difficulty dressing or bathing?
• Independent Living Disability (asked of persons ages 15 or older): Because of a physical, mental, or emotional condition, does this person have difficulty doing errands alone such as visiting a doctor’s office or shopping?

Generally speaking, the more questions used to identify disability, the more likely a person might be identified as an individual with a disability. A larger number of more detailed questionnaires likely do a better job in identifying specific disability types as well as information about health conditions that might not be elicited by a more basic set of questions. They may also be more likely to identify individuals who are less severely impacted by their disability or health issue.

Recently the revised SIPP adopted the same six questions used by the American Community Survey. As useful as the ACS six-question sequence is, it does not provide a very detailed perspective regarding specific disability types and limitations. For example, the ACS six-question sequence isn’t really designed to identify mental health issues, one of the more common disability types.

The Social Security Administration (SSA) found that only using the ACS six-question sequence was problematic for their purposes and funded a supplemental survey effort that compiled the detailed SIPP disability items into a follow-up SIPP supplemental survey. A new report based on the SSA’s Survey on Income and Program Participation (SIPP) SSA supplement was recently issued: Americans with Disabilities: 2014

A few points should be noted. The SSA supplement to the SIPP took a different approach to the previous SIPP in a number of ways. It was fielded as a separate survey rather than integrated into the SIPP. The response rate was lower and the items preceding the main “Adult Disability” section included some health and work disability items.

The SSA supplement resulted in a much higher estimate of the number and percentage of people with disabilities in the United States: 85.3 million people, or a 27.2% disability prevalence rate. The equivalent numbers from the 2010 SIPP were 56.7 million and 18.9%.

The main limitation of the SIPP SSA supplement data is that the relatively small sample size means that it can’t provide reliable state-level estimates. If you need either state- or local-level estimates, the best source is the American Community Survey.

All of this highlights the intricacies and challenges of producing a definitive number or percentage of people with disabilities in the United States. Even with years of experience doing research and crunching numbers, it can be tricky to give a final answer.

You can learn more about some of these surveys and their results at YTI's Disabilities Statistics web page.   

William Erickson, MS, is a Research Specialist at Cornell University’s K. Lisa Yang and Hock E. Tan Institute on Employment and Disability.