Functional status measures for integrating medical and social care

Abstract Purpose Identify standard self-report questions about functioning suitable for measuring disability across integrated health and social services. Theory Functional activities can be validly grouped according to the International Classification of Functioning, Disability and Health (ICF) chapters of mobility, self-care, and domestic life. Methods Cross-sectional analysis using information on 112,601 persons interviewed as part of the United States National Health Interview Survey on Disability. We combined related sets of questions and tested the appropriateness of their groupings through confirmatory factor analyses. Construct validity was addressed by seeking to confirm clinically logical relationships between the resulting functional scales and related health concepts, including number of physician contacts, number of bed days, perception of illness, and perception of disability. Results Internal consistency for the summed scales ranged from 0.78 to 0.92. Correlations between the functional scales and related concepts ranged from 0.12 to 0.52 in directions consistent with expectations. Conclusions Analyses supported the 3 ICF chapters. Discussions The routine collection of this core set of functions could enhance decision-making at the client, professional, organizational, and policy levels encouraging cooperation among the medical and social service sectors when caring for people with disabilities.


Introduction
Health of the individual, or the population as a whole, is not just about the reduction of premature injury, morbidity or mortality w1x. It is also about human functioning and the capacity of the person to participate in society. Recognizing the need for a standard way to describe disability concepts in 2001 the World Health Organization established the International Classification of Functioning, Disability and Health, known as the ICF w2x. The ICF is intended to comple-ment diagnostic information on aetiology, and morbidity included in its tenth revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-10) w3, 4x. The ICD-10 expresses patients' health conditions, while the ICF, through a separate coding taxonomy, describes the disabilities associated with them. To date there have been few empirical attempts to address how the complicated set of ICF codes might be applied in medical and social care. To be practical, it may be necessary to identify small sets of questions relating the most relevant information w5x. Our intent was to establish a core set of self-report measures of person-level functioning consistent with the ICF that would be sufficiently user friendly for routine collection by busy health care practitioners and social agencies.
Accepted by 191 countries, the ICF is fast becoming the international standard for describing health and disability. There are 2 broad classification categories-(1) Body Functions and Body Structures and (2) Activities and Participation-through which information is organized into chapters of related health concepts. All components within the ICF are quantified using the same generic scale which ranges from ''no difficulty'' through ''complete difficulty.'' This generic scale is presented as a means through which various assessment instruments can be calibrated w2x. Activity and Participation codes are organized into ''Chapters'' of related items. The ICF also includes environmental factors. These are known physical, social and attitudinal features surrounding the person that either hinder or facilitate potential for activity and participation.
The ICF, developed through the consensus of seven international WHO collaborating centres, is considered to be a classification scheme not a measurement system. The collaborative centres call for the ''development of assessment instruments for identification and measurement'' (p. 251) consistent with ICF concepts. The proposed core set of functions is presented as such an assessment instrument. The series of psychometric analyses to be presented here were necessary to provide evidence for validity of the proposed set of functional measures, and for the key ICF chapters they represent. Our method involves a confirmatory factor analysis applied to empirically test theoretically based constructs established through clinical logic and review of the literature.

Theoretical basis
The body function and structure components of the ICF reflect the types of information collected during routine medical review of systems. The core functions are being proposed as an analogous ''functional'' review of systems that are reflective of the Activity and Participation components. Mobility, self-care, and domestic life echo distinct well-established functional domains documented in the literature and were selected as the ICF chapters most fundamental to clinical objectives. Mobility includes motor functions (such as standing or reaching, etc.). These motor functions have been referred to as ''functional limitations'' and form the building blocks of more complex activities such as those included in the self-care and domestic life chapters w6x. Self-care describes basic ''activities of daily living or ADLs'', such as dressing or toileting, w7x and domestic life captures the more complex ''instrumental activities of daily living'', such as shopping or heavy housework w8x.
Within our conceptual framework these domains are partly hierarchical. Problems with mobility (the most basic functions) are primarily attributable to impairments in body function or structure, while difficulties with self-care or domestic life activities (the most complex) depend on interactions between those impairments and environmental barriers w9x. Figure 1 illustrates this conceptual framework with the core functions arranged by chapter as supported by the analyses described below. Widespread collection of responses to this core set of functions could aid clinicians and policy makers to make health care more responsive to the needs of individuals. It could improve the support of populations of people with disabilities by encouraging better linkage of health to social care services.

Data
The core set of functions was developed from questions on the 1994-1995 disability supplement of the National Health Interview Survey on Disability (NHIS-D) w10, 11x, originally intended to reflect the World Health Organization's International Classification of Impairment, Disabilities and Handicaps w12x that preceded the ICF. The NHIS-D is a cross-sectional, stratified, random, multi-staged probability sample representative of the United States (US) non-institutionalized population. We selected respondents 18 years of age and older (ns143,007). A random selection of 80% of the data was used (ns116,005). The remaining data were held back for cross validation of multivariate statistical models applying the core set of functions in subsequent analyses not presented here.

NHIS-D questions
The NHIS-D questionnaire obtained information about all members of households selected at random to be representative of the non-institutionalized population. It included questions about abilities to perform 20 routine activities rated as:

Factor analysis
We applied confirmatory factor analyses in order to empirically test the validity of the theoretical constructs described above. The factor analysis was to be considered successful in validating the hypothesized theoretical model if there was a clear clinical interpretation consistent with expectation for each identified latent factor. Sample weights were used to account for the multistage sampling design. Analyses began assessing the number of underlying latent dimensions necessary to adequately explain correlations among observed item scores. This was done by constructing a Scree plot of the incremental magnitudes of the eigenvalues determined from the correlation matrix versus their rank order. The cumulative sum of eigenvalues divided by the number of items reflects the total variance explained by that number of latent dimensions among the multiple items. The point where the incremental addition of another factor does not appreciably increase this variance indicates that the data do not support further increase in latent dimensionality. We hypothesized that the 20 NHIS-D ques-tions arose from the 4 latent domains expressed above. We further hypothesized correlations between the self-care and domestic life domains to be at least moderate. Therefore, the factor analytic model was determined after promax oblique factor rotation which allows for inter correlation among the factors. In general, the quality of a factor analytic solution is judged on the simplicity of the factor pattern matrix. The factor pattern matrix summarizes the magnitude of the associations between observed measures and underlying latent traits. A simple solution is one in which items tend to be highly associated with only one latent dimension. The objective of factor rotations is to select among the optimal factor pattern matrices, the one that has the simplest structure according to some criterion for 'simplicity'. Dimension-specific indices were constructed as sum scores from items with factor loading that were greater than 0.40. Factor solutions were obtained using SAS software version 8 w14x.

Summed scale analysis and item-total correlations
Cronbach's alpha w15x was used to measure the internal consistency of the constructed sum score scales w16x and to study the effect of deleting the item This article is published in a peer reviewed section of the International Journal of Integrated Care with the lowest item-total correlations. If removal significantly increased alpha, the item was excluded because its presence detracted from the internal consistency of the constructed sum score index.

Establishing population norms for the scales
The United States population is used to illustrate the process of establishing norms. The number of individuals per 10,000 in the United States who had at least some difficulty with one or more activities in each domain was determined using population weighted data. To calculate confidence limits, the standard error of estimated prevalence values were computed, taking into account the multi-stage sampling design through SUDAAN w17x. As a last step in scale development we translated mean index scores estimated from the 4-level NHIS-D items into 5-category ordinal scales consistent with the 5-level ICF paradigm. This 5-level scale reflects the ICF qualifiers of: no difficulty in any of the items (all scores by definition, were 1), mild difficulty (mean item score ranged from 1 to F1.5), moderate difficulty (mean item score ranged from 1.5 to F2.5), severe difficulty (mean item score ranged from 2.5 to F3.5), and complete difficulty (mean item score ranged from 3.5 to F4.0).

Validity
Construct validity of the scales was determined by testing for expected associations with other NHIS-D questions w10, 11x using Spearman rank correlations. The largest associations of the functional scores were expected with perception of disability. Smaller associations were expected with the numbers of physician contacts and the number of days the individual remained in bed at least half the day over the last year.

Results
There were 112, 601 subjects whose data were complete in all 20 activities used to form the scales. Over half (53.4%) were women, 56.4% were between the ages of 18 and 44 years, and 6.2% were over 75 years of age. Just under 2y3 of respondents were described as white. Table 1 characterizes the actual respondents included in this study, and shows the proportion of the population represented by each characteristic.

Item level analyses
Eating was the activity in which the fewest reported problems and walking 1/4 mile was the activity in which the largest number reported problems. At least some individuals were coded as functioning at each level in each of the 20 items.

Factor analysis
The Scree plot of eigenvalues identified a 4-factor solution as optimum. These first 4 eigenvalues summed to 70% of the total sum of the eigenvalues. The rotated factor pattern is shown in Table 2, supporting the 3 ICF chapters of mobility (factors 1 and 4), self care (factor 2) and domestic life (factor 3), with the mobility chapter further sub-divided into lower (factor 2) and upper body scales (factor 4), as expected. Review of the factor loadings of items associated with each factor shows all expected items met the minimum 0.40 criterion for belonging to their expected latent dimension. For example, loadings for the first factor ranged from 0.65 to 0.87. In contrast, factor loadings for those items identified as associated with factor 1 were close to zero with one exception. The factor 3 loading for ''heavy house work'' was 0.39, although still below the 0.40 criteria. This implies that this activity is multidimensionally associated with factor 3 as well as with factor 1. This activity hypothesized to be associated with items in the domestic life chapter (factor 3), was associated more strongly with lower body functions (factor 1). The ''reaching'' activity in upper body functions loaded weakly compared to the other activities in the upper body function (factor 4) domain. All other items loaded on the factors expected.
As anticipated, the largest inter-factor correlation was between self-care and domestic life, at 0.54. The next This article is published in a peer reviewed section of the International Journal of Integrated Care  respectively. These findings support the conceptual framework of measurement as diagrammed in Figure  1.
These concepts are organized by ICF Chapter into a simple self-report checklist that can be applied in the clinic ( Table 3).

Validity
Construct validity was supported by Spearman rank correlations between the functional limitation scores and perceived disability, ranging from 0.27 to 0.52; for bed days, from 0.10 to 0.20; for number of physician contacts, from 0.12 to 0.20; and for perceived health status, from 0.15 to 0.35. The generally larger correlations with the perceived disability construct were taken as evidence for construct validity. Table 4 estimates the United States population prevalence (per 10,000 persons) expected to have at least some difficulty performing one or more of the activities in each domain or chapter based on population weighted data. Problems with lower body functioning appear by far the most prevalent and self-care limitations the least.

Discussion
Results of our factor analyses support the core set of functional measures organized into the mobility, selfcare, and domestic life chapters bridging population level NHIS variables from the US with ICF concepts. By facilitating standard comparisons for clinical practice and program evaluation, we propose that this standard set of core functions can help link and coordinate care across general practitioners, rehabilitation professionals, and social services as well as acute and long term care sectors. The component scales appear to reflect distinct clinically relevant concepts that correlate expectedly with perceived disability, perceived illness, greater numbers of bed days, and increased physician utilization in the US supporting construct validity. The core set of functions are sufficiently parsimonious for acquisition during routine clinical encounters through patient self-report or proxy.  Appropriate use could express the effects of illnesses, injuries and interventions on life participation in ways that are meaningful to patients w18x and facilitate communication among the many professionals and organizations necessary in providing care to patients with disabilities and multiple needs. Once collected, the core functions could be disseminated through electronic formats across settings w19x and applied in multi-level analyses ( Figure 2). Uploads from the medical clinic to administrative databases with linkage to diagnostic information could enable population surveillance at the health plan, regional, and national levels. Such an ''information highway'' for centralizing medical and functional status information w20x has already been proposed by the Canadian government. All public, private, or voluntary health and social service organizations in an area could agree to partic-ipate in an umbrella system in efforts to enhance the coordination and efficiency of care for patients with multiple needs, while maintaining their own structures w21x.
The core set of functions might serve as a functional review of systems and routine screen for frailty. Physicians typically overlook the disabilities perceived by their patients w21x. Disability is associated with reduced use of preventive services, such as mammograms w22, 23x, the tendency to diagnose cancer at later stages w24x, and elevated risks of institutionalization and mortality w5, 25-28x. Specific interventions to help older people maintain independent functioning have shown benefits across multiple health, function, and quality of life domains w29-31x. The core functions were selected to be consistent with ICF concepts and to bridge content across measures typically applied in the acute w42, 43x, rehabilitative w44x, and long-term care settings w45x. Isolated difficulty with heavy housework and shopping will identify people with milder disabilities, while problems using the toilet and eating will identify those with more severe disabilities. Reliability of the core functional scales was consistent with commonly used health status instruments w46-50x. The core set is not intended to replace the more detailed setting-or conditionspecific instruments but rather to offer global indicators appropriate to linking and transmitting information across venues.
We end with several cautionary notes. Specific to each health system and nation, demonstrations will be needed to determine appropriateness of these measures to the proposed applications. We caution that it may not be reasonable to hold health care systems responsible for the functional deterioration of individual patients. While the linking of individuals' self-report functional status information to administrative databases could provide a ''powerful window'' for showing the effectiveness of the health care system w51x, use of such information has implications with regard to protecting individual privacy w52x and could be applied by payers to exclude populations of people whose disabilities (they believe) will likely cause high future expenditures. Ongoing debate is necessary on whether the value of collecting this type of information and enabling its reuse for administrative and policy purposes outweighs the potential economical and noneconomical costs of collection.