Measurement of the severity of disability in community-dwelling adults and older adults: interval-level measures for accurate comparisons in large survey data sets

Abstract

ObjectivesTo (1) create a single metric of disability using Rasch modelling to be used for comparing disability severity levels across groups and countries, (2) test whether the interval-level measures were invariant across countries, sociodemographic and health variables and (3) examine the gains in precision using interval-level measures relative to ordinal scores when discriminating between groups known to differ in disability.DesignCross-sectional, population-based study.Setting/participantsData were drawn from the Survey of Health, Ageing and Retirement in Europe (SHARE), including comparable data across 16 countries and involving 58 489 community-dwelling adults aged 50+.Main outcome measuresA single metric of disability composed of self-care and instrumental activities of daily living (IADLs) and functional limitations. We examined the construct validity through the fit to the Rasch model and the know-groups method. Reliability was examined using person separation reliability.ResultsThe single metric fulfilled the requirements of a strong hierarchical scale; was able to separate persons with different levels of disability; demonstrated invariance of the item hierarchy across countries; and was unbiased by age, gender and different health conditions. However, we found a blurred hierarchy of ADL and IADL tasks. Rasch-based measures yielded gains in relative precision (11–116%) in discriminating between groups with different medical conditions.ConclusionsEqual-interval measures, with person-invariance and item-invariance properties, provide epidemiologists and researchers with the opportunity to gain better insight into the hierarchical structure of functional disability, and yield more reliable and accurate estimates of disability across groups and countries. Interval-level measures of disability allow parametric statistical analysis to confidently examine the relationship between disability and continuous measures so frequent in health sciences (eg, cholesterol, blood pressure, C reactive protein).

Associations between community-level disaster exposure and individual-level changes in disability and risk of death for older Americans

“…First, it is recognised that the sum of ADLs and IADLs is likely to suffer from construct under-representation when used as a measure of disability (26). This refers to the fact that the ADL/IADL measure is likely to capture only part of the disability construct that we are truly interested in.…”

“…That is, the sum of ADLs and IADLs is likely to provide only an imperfect measure of functional disability, and is more likely to provide a measure of functional independence. Second, a measure based on ADLs and IADLs is likely to exhibit differential item functioning, especially with regards to age (26–28). This suggests that the response probabilities for specific ADL and IADL items may be affected by age-related characteristics of the individual that are not related to the underlying disability level.…”

“…This suggests that the response probabilities for specific ADL and IADL items may be affected by age-related characteristics of the individual that are not related to the underlying disability level. Whether this leads to the sum of ADLs and IADLs being a biased measure of the severity of disability is however uncertain (26, 28). …”

Condiciones de salud y factores relacionados con discapacidad en adultos mayores -Una reflexión para la atención-

“…Sin embargo, las instrumentales no fueron claramente más desafiantes que las AVD (por ejemplo, "manejar dinero" o "preparar una comida caliente") (11) . Del mismo modo, la localización de elementos para actividades aparentemente similares (por ejemplo, "caminar 100 metros" y "caminar por una habitación") fueron marcadamente diferentes (28) . En el análisis de los resultados, se detectó que los AM evaluados realizaban de manera independiente las medidas de higiene personal (bañarse sin ayuda, lavarse las manos y los pies); con relación a la toma de sus medicamentos, el 88,6% lo realizaba sin ayuda, preparaba su comida el 73,6% de manera autónoma, el 85,5% manejaba su propio dinero y el 70% hacía sus propias tareas de la casa.…”

Construct Validity of the Spanish Versions of the Memorial Symptom Assessment Scale Short Form and Condensed Form: Rasch Analysis of Responses in Oncology Outpatients

“…15 Moreover, the Rasch model allows easy comparisons of measures and easy health status interpretation in clinical and epidemiological studies. 15,16 The aim of this study was to evaluate the internal construct validity and reliability of the Spanish versions of the MSAS-SF and CMSAS in oncology outpatients. Specific aims of the study were to examine 1) response category functioning, 2) person-response validity, 3) item hierarchy and targeting, 4) model fit, 5) unidimensionality, 6) reliability, and 7) differential item functioning (DIF) by age, gender, and marital status.…”