Methodological challenges in measurements of functional ability in gerontological research. A review. (Avlund, 1997)

Avlund, K. (1997). Methodological challenges in measurements of functional ability in gerontological research. A review. Aging, 9(3), 164-174.

Department of Social Medicine and Psychosocial Health, University of Copenhagen, Denmark.

This article addresses two important challenges in the measurement of functional ability in gerontological research: the first challenge is to connect measurements to a theoretical frame of reference which enhances our understanding and interpretation of the collected data; the second relates to validity in all stages of the research from operationalization to meaningful follow-up measurements in longitudinal studies. Advantages and disadvantages in different methods to do the measurements of functional ability are described with main focus on frame of reference, operationalization, practical procedure, validity, discriminatory power, and responsiveness. In measures of functional ability it is recommended: 1) always to consider the theoretical frame of reference as part of the validation process (e.g., the theory of "The Disablement Process"; 2) always to assess whether the included activities and categories are meaningful to all people in the study population before they are combined into an index and before tests for construct validity; 3) not to combine mobility, PADL and IADL in the same index/scale; 4) not to use IADL as a health-related functional ability measure or, if used, to ask whether problems with IADL or non-performance of IADL are caused by health-related factors; 5) always to make analyses of functional ability for men and women separately as patterns of functional ability and patterns of associations between other variables and functional ability often vary for men and women; and 6) to exclude the dead in analyses of change in functional ability if the focus is on predictors of deterioration in functional ability.

http://www.ncbi.nlm.nih.gov/pubmed/9258374

My note:

Disability refers to the expression of a functional limitation in a social context.

For a given ability, disability occurs when there is a gap between personal capability and the demands of the activity. Disability can be alleviated from either side, by increasing capability or by reducing demand.

* Interesting thought about the standardized evaluation of disability: Someone who cannot manage shopping, because he or she lives too far away from the shopping center is disabled. But when a person moves to a place closer to the shopping center, she or he become non-disabled by this definition. 8-O

ADL is often used synonymously with PADL (physical activities of daily living).

How could functionality and disability be defined during interview and questionnaires?

• With or without difficulty
• With or without personal help
• Pain
• Reduced speed
• Tiredness
• Initiative
• With or without technical aids

The main issues relating to the measurement of ADL and IADL

• Disagreement about which activities goes where because whether a person perform a task is sometimes dependent on gender, culture, house condition etc. For instance, concerning disability involving cooking, up to the point of this writing, elder women seem to cook more than man. When a person report to not perform the cooking activity, it is because there is a lack of opportunities or because this person really have problem performing the cooking task. Similarly, when I said that I had not gone out for social functions since I had the spinal injuries, is it because the physical condition stopped me from attending these functions or is it because nobody asked? 8-O lol
• Second, should we measure maximal capacity or actual functional status
• Third, how do people evaluate the importance of being able to perform individual activities? For instance, is it more important for me to be able to walk around like ordinary people or to regain, first, my ability to lift up to 25 bls of weight?

Measurement procedure for functional ability

• Observation
• Performance
• Self-report
• Structured interview

Content validity

1. Content validity has to do with how well an instrument covers the full range of the domain
2. Most ADL/PADL measures are further development of Katz's Index of ADL
3. Most measures of IADL came from Lawton & Brody, who, recommended one 8-item scale for female and 5 for male.
4. A Canadian study showed the following reason for not performing the IADL tasks
   
   1. No need (e.g., no animal or garden for me to take care of)
   2. No need because someone else does it (e.g., my mama did cooking, grocery shopping)
   3. Doesn't know how to do it or not motivated to do it… (e.g., I take public transit in NYC… not driving)
   4. Physical inability (e.g., going up and down the hill)
   5. Fear of falling
   6. Environmental obstacles (e.g., the floor is slanted… not flat)
      
5. Old men don't cook? More associated with gender-role rather than functional disability
6. IADL differences were found among old people in different areas and countries. For instance, the reported performance of light household between people in Kuwait and West-Berlin. The plausible reason…. The report of "disability" might not due to the physical inability rather than where you live.

Construct validity

1. When the result of a measurement agrees with the theoretical expectations… we got construct validity.
2. Construct validity of a measure could be tested by the use of Factor analyses, Guttman Scalogram Analysis, and, Rasch model
3. Even though both PADL and IADL measure disability, it might cause some problems to combine by ADL and IADL in the same index.
4. Confounding results:
   
   1. Studies showing mobility forms a separate dimension
   2. ADL and IADL do not belong to the same dimension
   3. Unidimensional structure of ADL and IADL
5. The contradictory findings might be caused by differences in
   
   1. Questions
   2. Categories
   3. Statistic methods
   4. Sample population
6. Some studies distinguish functional disability into four categories
   
   1. able without difficulties
   2. Able with difficulty
   3. Able with help
   4. Not able at all

Discriminatory power

• The aim of a method may be the ability to distinguish
  
• The high functioning elderly from the medium or low
• Those with preclinical disability from these with real disability (? Is there such thing called fake disability? 8-O)
• Elderly people in different service setting
• Elderly people with different diseases
• Show variations within the single group such as the differential level of functioning among elderlies in senior homes
  
• Some functional ability scales are able to show differential discriminative effect for those with poorer functioning (sounds like the concept of α in Item Response theory to me)
• Is it possible the use a scale to assess the all range of functioning? (Item bank maybe?)
• What qualities are we trying to distinguish? Speed? Tiredness? Or Help?

The categories used are important. For instance able/not able" distinguish less than categories such as "able/able with difficulties/not able"…

Responsiveness

• Defined as the ability to detect change
  
  • IADL might be better suited for the detection of change
  • Mobility might be better suite in detecting changes in elderly than young people
• Stats related problem
• Ceiling or floor effect concerning improvement or decrease in functionality
• Inclusion of the dead in the measuring of change in functional ability…. 8-O
• Usefulness of functional ability measure
  
  • To measure consequences of the disease or condition
  • To detect risk group for earlier or preventative intervention
  • To evaluation the effect of intervention

• The types of intervention that directly affect demands and disability could be
• Modification of environment
• Activity accommodations
• External support
• Psycho-social factors
• Coping
  
• Recommendations of the authors about the measures of functional ability
  
  • There has to be a theoretical framework
  • Assess content validity before jumping into construct validity
  • Do not combine mobility, ADL/PADL and IADL in the same index
  • Always make sure that the performance problems associated with IADL are due to "physical disability"
  • Look for other differentiating factors such as gender or culture
  • Think about the impact of the dead in the study results