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Aggregated measures of functional disability in a nationally representative sample of disabled people: analysis of dimensionality according to gender and severity of disability

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Abstract

Objective

To determine (i) the dimensional invariance of instrumental and basic activities of daily living (IADL/ADL) by gender subgroups, and (ii) the extent to which ADL dimensionality varies with the inclusion or exclusion of nondisabled people.

Methods

Data were taken from the 1999 Spanish Survey on Disability, Impairment and State of Health. The analysis focussed on 6,522 people aged over 65 years who received help to perform or were unable to perform IADL/ADL items. Unidimensional and multidimensional item response theory (IRT) models were applied to this sample.

Results

In the female sample, IADL/ADL items formed a scale with sufficient unidimensionality to fit a two-parameter logistic IRT model. In the male sample, the structure was bidimensional: self-care and mobility, and household activities. When the sample was composed of IADL/ADL disabled people, ADL items formed a unidimensional scale; when it was composed only of ADL disabled people, they formed a bidimensional structure: self-care and mobility.

Conclusions

IADL/ADL items can be combined in a single scale to measure severity of functional disability in females, but not in males. Separate aggregated scores must be considered for each subdomain, basic mobility and self-care, in order to measure the severity of ADL disability.

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Abbreviations

1PL:

One-parameter logistic model

2PL:

Two-parameter logistic model

ADL:

Basic activities of daily living

AARC:

Average absolute residual correlations

DIF:

Differential item functioning

DWLS:

Diagonally weighted least-squares estimator

EDDES:

Survey on disability, impairment and state of health

FIFA:

Full information factor analysis

IADL:

Instrumental activities of daily living

IRT:

Item response theory

MNQS:

Mean square error statistics

ULS:

Unweighted least-squares estimator

WLS:

Generally weighted least-squares estimator

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Author information

Authors and Affiliations

  1. Department of Nursing, University of Alicante, Campus de San Vicente del Raspeig, Ap. 99, 03080, Alicante, Spain

    Julio Cabrero-García

  2. Department of Basic Psychology and Methodology, University of Murcia, Murcia, Spain

    José Antonio López-Pina

Authors
  1. Julio Cabrero-García
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  2. José Antonio López-Pina
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Corresponding author

Correspondence to Julio Cabrero-García.

Appendix

Appendix

English and Spanish versions of IADL/ADL items

English version of National Institute of Statistics (INE)

Extract of instructions for interviewers (interview contextual effect):

  • If you find that one person suffers from a disability or disabilities (for example, 5.2, stand up, lie down, stay in a standing or sitting position), read the entire list of disabilities related to the inside Mobility problem (5.1, 5.2 and 5.3) and, for each disability suffered, put a cross against YES.

IADL/ADL items:

  1. 5.

    Movement activities (moving around indoors)

    1. 5.1.

      Maintaining and changing body position (on lying down position) (body position changes).

    2. 5.2.

      Getting up, sitting down, and maintaining a standing or seated position (transfers).

    3. 5.3.

      Moving around your own home (walking indoors).

  2. 7.

    Moving around (except in own home) (moving around outside)

    1. 7.1.

      Moving around without using transport (walking outside).

    2. 7.2.

      Moving around using public transport (using public transportation).

  3. 8.

    Daily life activities (self-care)

    1. 8.1.

      Washing oneself and care of body parts (bathing).

    2. 8.2.

      Activities related to excretion (toileting).

    3. 8.3.

      Dressing (dressing).

    4. 8.4.

      Eating and drinking (eating and drinking).

  4. 9.

    Care of necessities and domestic activities (household activities)

    1. 9.1.

      Procuring and taking care of daily necessities (including shopping and supervision of supplies and services) (shopping).

    2. 9.2.

      Taking care of meals (preparing meals).

    3. 9.3.

      Laundry and caring for clothes and footwear (laundry).

    4. 9.4.

      Taking care of dwelling (housework).

    5. 9.5.

      Taking care of well-being of household members (caring for others).

Spanish original version

Extract of instructions for interviewers (interview contextual effect):

  • Si una persona sufre una o varias discapacidades (por ejemplo, 5.2., levantarse, acostarse, permanecer de pie o sentado) lea al entrevistado la lista completa de discapacidades de “Movilidad dentro de casa” (5.1, 5.2 y 5.3) y por cada discapacidad sufrida marque una cruz (X) en la casilla SI.

IADL/ADL items:

  1. 5.

    Movilidad dentro de casa

    1. 5.1.

      Cambios y mantenimiento de las posiciones del cuerpo.

    2. 5.2.

      Levantarse, acostarse, permanecer de pie o sentado.

    3. 5.3.

      Desplazamiento dentro del hogar.

  2. 7.

    Desplazarse fuera del hogar

    1. 7.1.

      Deambular sin medio de transporte.

    2. 7.2.

      Desplazarse en transportes públicos.

  3. 8.

    Cuidarse de sí mismo

    1. 8.1.

      Asearse sólo: lavar y cuidarse de su aspecto.

    2. 8.2.

      Control de sus necesidades y utilizar sólo el servicio.

    3. 8.3.

      Vestirse, desvestirse, arreglarse.

    4. 8.4.

      Comer y beber.

  4. 9.

    Realizar las tareas del hogar

    1. 9.1.

      Cuidarse de las compras y controlar los suministros y servicios.

    2. 9.2.

      Cuidarse de las comidas.

    3. 9.3.

      Cuidarse de la limpieza y planchado de la ropa.

    4. 9.4.

      Cuidarse de la limpieza y mantenimiento de la casa.

    5. 9.5.

      Cuidarse del bienestar de los demás miembros de la familia.

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Cabrero-García, J., López-Pina, J.A. Aggregated measures of functional disability in a nationally representative sample of disabled people: analysis of dimensionality according to gender and severity of disability. Qual Life Res 17, 425–436 (2008). https://doi.org/10.1007/s11136-008-9313-x

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  • DOI: https://doi.org/10.1007/s11136-008-9313-x

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