Journal Issue: Children with Disabilities Volume 22 Number 1 Spring 2012
Prevalence and Trends of Disability for U.S. Children
Information on the prevalence and trends of childhood disability is needed to formulate effective policies for preventing new cases of disability and ameliorating the impact of existing cases. Various national surveys collect information on the prevalence of chronic conditions, impairments, and disabilities among children. These include the National Survey of Children's Health, National Survey of Children with Special Health Care Needs, National Health and Nutrition Examination Survey, Medical Expenditure Panel Survey, and National Health Interview Survey, or NHIS, from the U.S. Department of Health and Human Services as well as Census Bureau surveys such as the American Community Survey and the Survey of Income and Program Participation. Each survey is conducted for a different purpose, and some have been used to measure the broader concept of special health care needs, but all incorporate at least some general measures of disability based on different combinations of items that capture functional or activity limitation. These surveys share certain limitations such as reliance on subjective parental reports, exclusion of individuals living in institutional settings, and lack of a standardized measure of childhood disability that fully captures the multidimensional nature of disability. Table 1 shows recent prevalence estimates derived from different national surveys and the various ways disability has been measured by survey methodologists and researchers. As the table shows, measurement of childhood disability in the United States has lagged behind the development of the conceptual models described here. Instead, most measures incorporated in current national surveys continue to use modified medical approaches.
Although less than ideal, the concept of limitation of activity used in the NHIS offers the most inclusive approach to measuring disability among the existing national surveys. The NHIS measure is designed to identify children who experience limitations in developmentally appropriate activities. Like disability measures in other national surveys, it does less well in capturing the participation dimension of disability. The NHIS measure offers the advantage of being continuously collected over the past fifty years, albeit with some changes in measurement methodology. Because of its inclusiveness and longevity, we use it here to describe prevalence and trends in childhood disability.
The NHIS measure of limitation in usual activities is a composite of several developmentally appropriate items that capture social role limitations (play for preschool-age children and school for older children). In recent years these items have been complemented with several measures of functional status (activities of daily living and difficulties with mobility and memory). A catch-all item is meant to identify any other limitations. Using this approach, any child under age eighteen is initially classified as being limited in usual activities if he or she is reported to receive special education or early intervention services; experience difficulty walking without equipment; experience difficulty remembering; or have any other limitation. Children under five are also considered to be limited in usual activities if they experience limitations in the kinds or amounts of play activities done by other children, as are children aged three and older who need help with personal care including bathing, dressing, eating, getting in and out of bed and chairs, using the toilet, and moving around the home.
When a child meets any of these criteria, the respondent is then asked to identify the condition(s) causing the limitation. Reported conditions are classified by the data collection agency as "chronic," "not chronic," or "unknown if chronic." In this section we report on the prevalence of limitation in usual activities due to one or more chronic conditions. We use the terms "limitation in usual activities due to one or more chronic conditions" and "activity limitations" interchangeably.
Current Prevalence Estimates from the NHIS
The prevalence of activity limitations overall and for subgroups of the population is shown in table 2 and is based on NHIS data for 2008–09. On average for the two years, the prevalence of activity limitations for children younger than eighteen was 7.7 percent. Nationally, an annual average of 5.7 million children was estimated to have an activity limitation in 2008–09. Data from other sources indicate that these children represent a relatively small subset of the population of children with chronic conditions. Studies conducted with data from the late 1980s indicate that more than 30 percent of children experience one or more chronic conditions over the course of a year.40 More recent national survey data indicate that up to half of all children experience chronic conditions over a multiyear period.41
The prevalence of reported activity limitations varies by demographic and socioeconomic characteristics (see table 2). For example, children aged six through eleven have double the prevalence of activity limitations as children under six. This tendency has been observed in past studies from the NHIS and likely reflects the added demands placed on children as they enter school and possibly increased recognition of certain conditions such as learning disabilities. Prevalence does not vary much across age groups once children are of school age. Boys are almost twice as likely as girls to be reported as having a limitation. Activity limitations are reported less frequently for black and white children than for Hispanic and Asian children. There is a substantial, though somewhat uneven, income gradient; children living in families with incomes below the federal poverty level (FPL) are almost twice as likely to be reported with activity limitations as children in families with incomes at 400 percent or more of the poverty level. Children in families where the highest parental educational attainment is less than college were more likely to be reported with activity limitations than those with one or more parents who had completed college. Finally, children in single-mother families were more likely to be reported with activity limitations than children in other household types. For the most part, these demographic and socioeconomic differences are consistent with past reports.42
Conditions Associated with Limitations in Usual Activities
Prevalence estimates for individual diagnostic categories are presented in table 3. The first column displays the average annual prevalence of chronic conditions reported as causes of activity limitations in 2008–09. The conditions in table 3 reflect main and secondary causes of activity limitations, hence, the sum of condition prevalence estimates exceeds 100. In fact, an average of 1.4 conditions was reported for each child with activity limitation. The top five conditions are primarily developmental, emotional, and behavioral. Speech problems, learning disability, and ADHD were each cited by more than one in five parents as contributing to their child's activity limitation. The most common physical health condition was asthma, which was reported as a cause of activity limitations for 8 percent of all children with limitations. Most of the other conditions listed in table 3 affected comparatively small numbers of children.
The dominance of developmental, emotional, and behavioral conditions over the traditional physical conditions as causes of childhood activity limitations has important implications for the design of effective prevention and intervention programs. When most of the current programs serving children with disabilities were designed, the most prevalent causes of disability were physical conditions. This epidemiological shift and its implications are discussed in more detail later in this article.
Trends in Childhood Activity Limitations Due to Chronic Conditions
A growing body of studies has documented an increase in the prevalence of a variety of reported childhood chronic conditions over time, including increases in asthma, autism, and behavioral conditions such as ADHD.43
An analysis of data from the Digest of Education Statistics shows a near doubling of the share of students with diagnosed disabilities between 1976 and 2005, with a modest decline between 2005 and 2009.44 Past studies have also demonstrated substantial increases in the prevalence of reported childhood activity limitations. One analysis, for example, documented a doubling in the prevalence of activity limitations for children under age seventeen between 1960 and 1981, from 1.8 percent to 3.8 percent, using data from the NHIS.45 More recent NHIS data show that the upward trend in activity limitations has continued (figure 1). The prevalence for children under age eighteen again more than doubled, from 3.8 percent in 1981 to 8.0 percent in 2009 (the age range used to define children in the NHIS was changed from under seventeen to under eighteen in 1982). Overall, the data in figure 1 indicate a fourfold increase in prevalence of childhood activity limitations during the past half century. Figure 1 also shows some of the major programmatic initiatives enacted during this period along with the dates of major revisions to the NHIS survey questionnaire. Because the activity limitations are defined in part by the receipt of services, the extent to which increases in reported disability may be driven by increases in service provision is an open question. These trends are discussed in more detail later.
Trends by Social Class
Monitoring the magnitude of social disparities in health across time is an important way to determine if the country is meeting public health goals to reduce these disparities. A comparison of prevalence ratios for childhood activity limitations due to chronic conditions, as measured by the NHIS over a forty-five-year period, indicates that the magnitude of the differential between the poor and the nonpoor remained roughly the same, even as children in both income groups experienced a near fourfold increase in prevalence during the period. In 1964 poor children were one and a half times more likely than those in nonpoor families to have an activity limitation attributable to chronic conditions (3.1 percent versus 2.0 percent).46 These ratios held nearly constant at 1.41 in 1978 (5.2 percent vs. 3.7 percent), 1.68 in 1992–94 (9.6 percent vs. 5.7 percent), and 1.50 in the 2008–09 NHIS (10.8 percent vs. 7.4 percent).
Trends by Condition
As indicated earlier, the leading conditions associated with activity limitations in 2008–09 were largely developmental, emotional, and behavioral in nature. Comparison with earlier time periods is made difficult by changes in the way condition data are collected and coded in the NHIS. Before 1996 respondents were asked to name the main and secondary causes of activity limitation. Trained diagnostic coders at the National Center for Health Statistics then categorized reported conditions into detailed International Classification of Disease codes. The NHIS no longer distinguishes main and secondary causes, and only the broad categories of conditions shown in table 3 are collected for children. Nevertheless, some conclusions, albeit provisional, may be drawn concerning changing patterns of conditions. The leading causes of activity limitation for 1979–81, 1992–94, and 2008–09 are shown in table 4. Over this thirty-year period, the composition of activity limitations has changed dramatically, with physical health conditions, formerly dominant, receding in importance as developmental, emotional, and behavioral conditions became the leading causes of childhood activity limitation.
Given increasing trends in childhood disability in the United States, it is useful to consider how the United States compares with other nations with similar social and economic conditions. Cross-national comparisons of child health and education outcomes are often used to assess how differences in culture, geography, health, and social systems shape child outcomes. Comparing U.S. data on the prevalence and trends in childhood disability with those of other nations is also quite revealing regarding similarities and differences. A recent report from the Organization for Economic Cooperation and Development (OECD) attempts to harmonize the results of different data collection efforts in member countries.47 This analysis reveals that the United States is similar in many ways to other OECD countries but has higher rates of autism and twice the rate of speech and language difficulties. This latter difference, however, appears to be driven by differences in classification schemes between the United States and Europe.48 The larger proportion of children classified with autism in the United States may be the result of several factors, including recent changes in the U.S. diagnostic rubric for autism.