Mental health can be defined as “a dynamic state of internal equilibrium which enables individuals to use their abilities in harmony with universal values of society” (pp. 231-232).1 This includes the capabilities necessary for individuals to fully participate in their communities and to fulfill the social roles of their choosing. Adopting such a definition makes clear the importance of mental health for all people to optimally and effectively support well-being. Disability, however, can interfere with one’s ability to function in society according to societal norms due to inaccessible and ableist systems.2 These obstacles to social participation can be damaging to mental health.

How disability is defined and conceptualized can have profound impacts on findings and their interpretation.3 This paper uses both the social model of disability and the biopsychosocial framework of the International Classification of Functioning, Disability and Health (ICF). The social model of disability contends that disability is primarily the result of inaccessible barriers in society, rather than the physical or mental impairment itself. While disability is also uniquely experienced by each individual, research considering a broad range of disability types can help inform interventions at the societal level which have the potential for greater and more effective impact.4 The biopsychosocial framework of the ICF similarly conceptualizes disability as shaped by both individual medical or health problems and the ability to function within the environment. Considering disability in terms of functional disability, or difficulty with daily activities, rather than diagnosis, thus allows for a broader consideration of how both individual diagnoses and societal structures intersect to construct disability.5 Conceptualizing disability in terms of functioning, rather than solely based on diagnosis, is an approach that contextualizes disability broadly within the social context, allowing for identification of overarching trends. Importantly, within the US policy context, disability definitions that are used for benefit determinations by the Social Security Administration are primarily based on functional disability rather than diagnostic status.

Studying specific diagnoses and disabilities is essential for providing useful, specific insights, however, using functional disability instead allows for the evaluation of disparities at the national level of a group that is typically treated as homogenous within systems and by policy. Reduced group specificity is compensated for with understanding of national-level trends using disability constructs that mirror how policy often identifies disability and greater feasibility.

There are similarly many methods for measuring mental health symptoms and concerns. National surveys tend typically use validated psychological distress scales due to their ability to identify prevalence of common psychological symptoms that are often associated with an impact on social functioning and additional health care use and costs.6 Such scales are often preferred to self-report of mental health status as validated scales like the Kessler 6 and the Patient Health Questionnaire have stronger associations with limitations fulfilling one’s emotional or physical role.7 These symptom-based measures allow better identification of symptom prevalence in the population than diagnostic counts as they reflect current mental health status.8

Previous research into the association between disability and mental health largely finds that mental health symptoms are elevated in disabled people.1 Studies of mental health and disability in the United States using national data have used different measures of disability and mental health and/or were conducted prior to the COVID-19 pandemic. When disability was defined using functional disability, disabled adults were found to be at greater risk of both depression and anxiety, with frequent mental distress at a rate about 4 times greater than non-disabled adults. This disparity was even greater for disabled adults who are low-income.10 Another study used mental health to examine the association between functional disability and mental distress and found significant positive associations between almost all functional difficulty categories and mental distress.11

Existing studies about mental health and disability from the COVID-19 pandemic have found that the mental health impact of the COVID-19 pandemic was greater for those with disabilities than those without when defining disability with functional difficulties12 (e.g., functional disability) or using specific diagnoses.13, 14 Prior to the pandemic, studies of specific diagnoses, rather than studies of functional disability, found positive associations between depression and intellectual disability, autism, chronic pain, limb amputation, and self-reported physical disabilities, though this list is not comprehensive.15, 16, 17, 18, 19 In addition to increased odds of depression in individuals with chronic medical conditions, depression concurrent to such chronic medical conditions has been found to be associated with increased functional disability and lowered productivity.20 Sareen et al. further found significant associations between anxiety and numerous physical health problems often identified with disability and co-occurrence of anxiety and such diagnoses was associated with worse scores on quality of life assessments.21

Some research suggests that the elevated rates of mental health problems in the disabled population are likely more attributable to environmental factors than disability itself. In a study of British adults with intellectual disabilities, the elevated risk of mental health problems was almost entirely eliminated when controlling for age, gender, and socioeconomic indicators.22 Honey et al. found that there are minimal mental health differences for young people with a long-term, disabling health condition when controlling for level of social support and financial hardship.23

Further research is needed, however, to better understand this connection between mental health and disability at a population level. While some of the existing research about mental health and disability uses a functional definition of disability, the majority of existing research uses specific diagnoses or categories of diagnoses to understand the connection. While doing so allows study of clearly defined groups and disabilities, it neglects many of the more ubiquitous and pervasive experiences of disability related to policy. Furthermore, much prior research was qualitative or used a smaller sample size, limiting generalizability, and many prior studies occurred outside the United States.

This study adopts a broad conceptualization of disability by using a measure based on functional disability which can perhaps provide a more systems- or policy-level understanding of the daily experience of this group. This paper seeks to estimate the incidence of depression, anxiety, and psychological distress across disability groups using the National Health Interview Survey (NHIS) and the United Nations Washington Group Short Set on Functioning (WG-SS). We employed two measures of disability to demonstrate how different operationalizations of disability can yield different results. The WG-SS identifies disability based on functional difficulties or the lack thereof with six universal basic activities (e.g. functional disability). The WG-SS allows for creating both a binary and continuum measure of disability.24 While such a measure limits the ability to look at specific disability types, it allows for cross-national comparison and provides a nationally representative sample of the community-dwelling population in the US.

Given that disability diagnoses are often associated with more mental health symptoms, we hypothesized that greater functional disability would be associated with a higher frequency of mental health symptoms and psychological distress, regardless of formal diagnosis of either depression or anxiety. By using NHIS data, we have access to a larger sample than prior work and this allows for prevalence estimates for the United States.