Dimensionality and hierarchical structure of disability measurement. (van Boxel, Roest, Bergen, & Stam, 1995)

van Boxel, Y. J., Roest, F. H., Bergen, M. P., & Stam, H. J. (1995). Dimensionality and hierarchical structure of disability measurement. Archives of Physical Medicine and Rehabilitation, 76(12), 1152-1155.

Institute of Physical Medicine and Rehabilitation, Erasmus University Rotterdam, The Netherlands.

Since the D-code of the International Classification of Impairments, Disabilities, and Handicaps (ICIDH) in its full form has proven to be impractical, an instrument based on a selection of 28 items is used to measure disability in Dutch patients undergoing rehabilitation. The items are categorized into 5 domains of physical, activities of daily living (ADL), social, psychological, and communicative activity. Measurement is made on a 4-point scale ranging from 0 (not disabled) to 3 (severely disabled). As a result of the ordinal character of the rating, statistical and mathematical manipulations of the scores are complicated. The aim of this study was to obtain more insight in the dimensionality and hierarchical structure of the items, to overcome problems in comparing disability between items, between patients, and within patients between different moments in time. Mokken scale analysis of the disability scores from 1,967 rehabilitation inpatients showed that the 28 items constitute hierarchical scales. However, categorization of the items into the 5 original domains was not replicated. Five other scales or dimensions were investigated, measuring the level of extended ADL, extended psychological, fine motoric, work/leisure, and hearing/seeing activity, respectively. The number of items per dimension ranges from 14 in the extended ADL dimension to 2 each in the work/leisure and hearing/seeing dimensions. Although each disability item may be of importance in clinical case management, a reduced set of extended ADL items suffices to describe the disability level in this dimension for epidemiological research purposes. The other dimensions need further specification to provide reliable and sensitive measuring of disability.

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Notes

Introduction

• The authors thought that the concept of disability should have breadth and it is needed to incorporate indicators from multiple domains. For instance, in this study, the authors included 28 items from ICIDH (International Classification of Impairments, Disabilities, and Handicaps); these items fall into 5 domains including physical activity, activity in daily life, social activity, psychological activity and communication.
• This instrument uses a 4-point ordinal scale to rate individual's disability level with 0 indicating not disabled and 3 indicating severely disabled.
• Dimensionality is defined as the extent to which scale items can be combined to provide information on the same dimension. (Wright & Linacre, 1989)
  
  
  1. Wright BD, Linacre JM. Observations are always ordinal; measurements, however, must be interval. Arch Phys Med Rehabil 1989;70:857-60.
     

Physical activity

• Transfer lying-sitting
• Transfer sitting

Daily life activity (ADL)

• Feeding

Standing

• Walking indoors
• Walking outdoors
• Climbing stairs
• Reaching
• Manipulating
• Endurance
• Bending
• Lifting

Using lavatory

• Bathing
• Clothing

Psychological activity

• Orientation
• Memory
• attention
• Behavior
• mood
• Learning abilities

Communication

• Understanding speech
• Talking
• Hearing
• Seeing
• Writing

Social activity

1. Transport
2. Housing*
3. Employment
4. Family role
5. Recreation

Analysis

• Dutch inpatients during hospitalization
• The authors used a computer program called MSP to conduct Mokken scale analysis for polychotomous items.
• Given the ordinal nature, Spearman's rank correlation coefficient or Spearman's rho was used to assess the reliability of the scales. (SPSS).
• Results of this study fail to reconstruct the original 5-factor structure. The new categorization consist of 5 new subdomainS: extended ADL, extended psychological activities, fine motoric activities, work/leisure activities, and hearing/seeing activities, respectively.