Saturday, January 2, 2010

American Community Survey (2003): Disabilities Nationwide

In a previous post, I took a quick look at how the total household population figure in the American Community Survey (ACS) for 2003 was calculated.  The numbers involved are not precise in every case, but the general concept appears to be that the "resident population" is divided into people who live in households and those who live in group quarters (e.g., prisons, hospitals, dormitories).  In the 2003 ACS, only households were examined.  The total number of people in the U.S. who were living in households in 2003 was estimated to be 282,909,885.  Of those, an estimated 176,395,446 fell into the traditionally defined working-age population aged 18-64.

The next thing to figure out, in moving toward statistics on disabilities at the county level, was how many of those 176,395,446 people were considered to have various kinds of disabilities.  Here, as before, I relied on the analysis of 2003 ACS data provided by Weathers (2005) in his Guide to Disability Statistics from the American Community Survey.  The previous post notes that the ACS understates disabilities when compared to some other national surveys; however, it has the advantage of being updated on the county level, and thus provides an essential stepping-stone in this investigation.

Weathers (2005) divides that total of 176,395,446 working-age people into those with (12%) and without (88%) disabilities, as defined by the ACS.  Weathers further narrows the working-age population down to the 25-61 age range, considering the 18-24 group as being of a "school-to-work transition age" and the 62-64 group as being of "early Social Security retirement age" (p. 19).  Since the 25-61 group accounts for 83% (i.e., 17,146,845) of the total of 20,609,733 people with disabilities in the larger 18-64 group (p. 54), I will tend to focus on that 25-61 group in this post.

To summarize, then, the ACS gives us, in 2003, an estimated 17,146,845 U.S. residents who lived in households (as distinct from group homes), had one or more disabilities, and fell into the 25-61 age group.  These people comprised roughly 10% of the estimated working-age (18-64) population of about 176 million.

According to Weathers (2005, p. 35), the ACS draws upon World Health Organization (WHO) concepts of impairment, activity limitation, and participation restriction, as expressed in the International Classification of Functioning, Disability and Health (ICF) (pp. 4-5).  In the ICF, Weathers says, an impairment is a significant deviation or loss in body function or structure (e.g., vision loss).  An activity limitation is difficulty in executing activities of daily living (e.g., dressing).  A participation restriction is a problem that a person may have in a life situation (e.g., lack of employer accommodation to the person's severe health condition).

As Weathers (2005, pp. 10-11, 35) describes, the ACS uses six questions to operationalize those ICF concepts.  Three of the six ask about impairments:  sensory, physical, or mental.  One asks about activity limitation, in the form of an inability to care for oneself inside one’s home.  Two ask about participation restrictions, in the form of physical, mental, or emotional conditions that prevent the person from going outside the home (e.g., to shop) or from working at a job or business.  The ACS defines disabilities as the presence of any one or more of these kinds of disability. As an example of how these questions may fail to count some disabilities, Weathers (p. 27) indicates that the question of going outside the home, used on the ACS, is narrower than the concept of Instrumental Activities of Daily Living (IADLs) used in some surveys.

The 2003 ACS data indicate that, for the 25-61 group, two of these six questions (pertaining to physical impairment and employment restriction) account for 55% of all disabilities.  Those two plus the next most frequently cited disability, regarding mental impairment, account for 70% of all disabilities in that age group.  Yet within that statement lies an interesting age-related permutation.  First, as one might expect, age is a factor in the calculation of disability under the ACS.  The data show that disability prevalence rates rise from 6.3 in the 5-17 group (that is, 6.3% of people in that age group have a disability) to 39.9 in the 65+ group (Weathers, 2005, p. 39).  At the same time, however, while those top three questions account for about 70% of disabilities in all three working age groups (i.e., 18-24, 25-61, and 62-64), the share due to mental impairments steadily declines.  Mental impairments constitute 30% of all disabilities in the 18-24 group, but only 15% in the 25-61 group and 10% in the 62-64 group.

It is not that mental impairments actually decline with age, though that may be the case for some kinds of mental impairments.  It is, rather, that mental impairments rise only slightly, from 3.7 in the 18-24 group to 5.8 in the 62-64 group.  This is quite different from the ninefold rise in physical disabilities between those two groups.  One explanation for that contrast is that the ACS may undercount mental disabilities in adults.  There is evidence of reduced awareness of mental disability on the part of adults and their primary care physicians (e.g., Surman, Wigal, & Lakes, 2009).  Undercounting of mental disabilities in adults would also be unsurprising if significant mental disabilities are incompletely conceptualized among adults (e.g., Nijmeijer et al., 2008, p. 701).

So far in this series of posts on statistics pertaining to disabilities, I have rarely gone beyond the relatively general descriptive approach provided by commentators such as Weathers (2005).  The preceding paragraph suggests, though, that a look at more critical or focused literature may highlight a number of shortcomings with the ACS, for purposes of counting disabilities.  As an example of another area in which a more refined approach may considerably enhance the statistical picture, one may review Weathers's remark (above) about the refinement that the IADL concept adds to the question of going outside the home.  Unless Weathers meant to contrast IADL against the ACS's question regarding self-care, and simply misspeaks on that point (compare pp. 27 and 39), it seems appropriate to question the finding that 6.9% of people in the 25-61 age group experience a significant employment restriction due to disability, and yet only 2.0% report a limitation in their self-care activity.  Without a boss or other reminder of a set goal, people at home may be more likely to adjust their goals and lives to accommodate their disabilities.

Those examples of potential shortcomings in the ACS may or may not be borne out in the professional literature.  I can't say; I haven't gotten that far yet.  The purpose of those remarks was simply to highlight a few ways in which the ACS may undercount disabilities.  Having achieved that, the next step in this investigation is to move from the national-level ACS data to the state level.