Functional limitations

Functional limitations

LASA filenames:
LASA030 / LASA230
LASA603 / LASA703
LASA183
LASEs803 / LASAEs903
LASEt603 / LASEt703

Contact: Dorly Deeg

Background
In the disablement process, functional limitations form the link between impairment and disability [Verbruge & Jette, 1994]. Impairments are dysfunctions and significant structural abnormalities in specific body systems. Functional limitations are restrictions in performing fundamental physical and mental actions used in daily life such as mobility (physical) or memory (mental). They are often expressed as difficulty doing activities. Disability is restriction in doing activities of daily living in any domain of life, in particular in fulfilling roles such as housekeeping, working, or caregiving. This is often expressed as need of help doing daily activities.

The measurement of functional limitations and activities of daily living can be based either on self-reports, or on observation of actual performance using physical performance tests. For functional limitations, both are available in LASA. The following considerations may be helpful in deciding which to use when dealing with a specific research question.

Whereas performance tests assess actual physical functioning at a specific moment, questionnaires on functional limitations assess functioning averaged over a longer period of time and in different environments [Myers et al 1993]. Accordingly, they come closer to covering true daily functioning than performance tests. Note, however, that questions on functional limitations assess potential or hypothetical ability because they are phrased not in terms of ‘do’ but in terms of ‘can’. The responses to these questions may be more sensitive to personal factors (mood, perceived competence) than performance tests [Kempen et al 1996]. Some authors consider performance tests as assessing hypothetical ability as well because of their experimental nature [Glass 1998]. On the positive side, because of their greater sensitivity in the higher ability range, timed performance tests are able to detect functional decline that is still imperceptible to respondents and thus not picked up by self-reports [Guralnik et al 1989]. As such, they are conceptually closer to functional limitations than to disability [Van Gool et al 2005].

Measurement instruments in LASA
The literature shows an enormous variation in the operationalization and assessment of disability. Across surveys, there are differences in the type, number, meaning, and response categories [Pluijm et al 2005]. The selection of items in LASA is based on consideration of the items in two long-standing disability indicators that have been used in cross-national research: the 6-item Capacity for Self-Care indicator [Shanas 1974] and the 9-item Organisation for European Cooperation and Development (OECD) indicator. The OECD indicator was translated into Dutch and validated by Statistics Netherlands [Van Sonsbeek, 1988]. It is used in the continuous Netherlands Health Interview Survey. The test-retest reliability of the Dutch version is reported by Boshuizen et al [2000]. The aim of the selection procedure was to achieve a parsimonious set of items [Verbrugge 1999].

Initial selection
In pilot studies prior to the start of the first LASA cycle [Smits et al., 1997], using iterative elimination, the item with the lowest item-rest correlation was omitted until three items were left. The selected activities are expected to be sensitive to changes over time, because they indicate mild levels of functional limitation. The three items that proved to form the best scale included:

Can you walk up and down a staircase of 15 steps without resting?
Can you use your own or public transportation?
Can you cut your own toenails?

Response categories used in LASA-B were:
0. Yes, without difficulty
1. Yes, with difficulty
2. Only with help
3. No, I cannot

The items can be summed to a scale using various options:

1. Defining functional limitations: counting the number of items ‘with difficulty’ or worse (range 0-3, internal reliability 0.73)
2. Defining disability: counting the number of items ‘with help’ or worse (range 0-3, internal reliability 0.71)
3. Defining mild versus severe disability: mild disability is defined as difficulty with one or more activities (i.e. response option 1), but able to perform all activities independently (i.e. never response options 2 or 3); severe disability is defined as not able to perform at least one activity independently (i.e. response options 2 or 3).
4. Functional limitations scale: summing the items irrespective of the content of the response categories (range 0-9, internal reliability 0.77).

The first option is considered to indicate functional limitations in terms of difficulty, the second to indicate disability in terms of help needed; the third scale separates functional limitations as mild disability and disability as severe disability; option 4 combines these two aspects with the advantage that the greater range enables better differentiation.

It should be noted that the three items are selected to represent the larger concept of functional limitations, and should not be used as single items. Kriegsman and colleagues (1997) examined the factor structure of the three items for specific chronic disease groups. The factor structures were comparable across groups, implying that summing the three item scores results in a global index of functional limitations, which is equally valid for each of the specific chronic disease groups studied.

Additional items
By the second LASA cycle (LASA-C), it was felt that three items might not be sufficient to catch aging-related declines in physical functioning. The three items were then supplemented with three items that were used in the NESTOR-LSN-study:

Can you dress and undress yourself?
Can you sit down and stand up from a chair?
Can you walk outside during five minutes without stopping?

The first two of these questions are generally considered as activities of daily living (ADL’s), rather than functional limitations [Katz et al., 1963; Lawton & Brody, 1969]. However, the borderline between restrictions in actions and in activities is very thin [Kempen & Suurmeijer, 1990]. The three questions correspond to three tests of physical performance as included in LASA.

Since the response categories of the LSN-items numbered five rather than four, from the second LASA-cycle, all items were asked with five response categories to obtain optimal differentiation:
0. Yes, without difficulty
1. Yes, with some difficulty
2. Yes, with much difficulty
3. Only with help
4. No, I cannot

Again, the total of six items can be summed to a scale in three ways:

1. Defining functional limitations: counting the number of items ‘with some difficulty’ or worse (for 6 items: range 0-6, internal reliability 0.85), or ‘with much difficulty’ or worse (range 0-6, internal reliability 0.84)
2. Defining disability: counting the number of items ‘with help’ of worse (range 0-6, internal reliability 0.80)
3. Defining mild versus severe disability: mild disability is defined as difficulty with one or more activities (i.e. response options 1 or 2), but able to perform all activities independently (i.e. never response options 3 or 4); severe disability is defined as not able to perform at least one activity independently (i.e. response options 3 or 4).
4. Functional limitations scale: summing the items irrespective of the content of the response categories (range 0-24, internal reliability 0.85).

In these scales, low scores indicate few limitations, and high scores, many limitations.
Note that options 1) and 3) count items with ‘some difficulty’ from LASA-C onwards, which may not capture the same degree of limitations as just ‘difficulty’ at LASA-B. Thus, this option does not yield measures that are comparable across all LASA-cycles. This problem does not exist using option 2). To make the sum scores of option 4) comparable to LASA-B, one can use for LASA-B the sum score of six items based on the available items at LASA-B plus an imputation based on LSN-A (measured 10 months earlier) for the remaining items. Alternatively, the original three items can be used, but the five response categories now add up to 12 instead of 9. This can be aligned by multiplying the sum score by ¾ from LASA-C onwards (see Appendix 1).

Starting with the baseline cycle of the LASA-cohort recruited in 2002, a seventh item was added to improve possibilities for international comparison [Pluijm et al., 2005]:
– Can you take a shower or bath?
This item again has five response categories (see LAS2B030).

Limitations in joint mobility
Another 12 items on functional limitations are available focusing on activities that are particularly restricted by joint disorders, such as reaching above the shoulder and picking up an object from the floor [Raspe et al., 1990; Kohlmann & Raspe, 1994]. These are included in the medical interview for the study of Falls and Fractures in waves C, D, and E (LASA183: mlimshelf through mlimrun). Response options are: 1) no difficulty, 2) a little difficulty, 3) only with help.

Use of assistive devices, assistance, and avoidance
The use of assistive devices was determined by a branching question following each item, asking if the respondent used an assistive device for this activity (response options: 1) no, 2) yes). This is the recommended approach to assess the use of assistive devices [Agree et al., 2003].

The use of personal assistance was determined by a second branching question following each item (response options: 1) no, 2) yes). A further branching question asked about the frequency of this assistance: 1) never, 2) rarely, 3) sometimes, 4) often or always.

Questions on assistive devices and personal assistance were not asked of respondents who reported not being able to do the activity at all.

The usual questions on functional limitations may not capture the early beginnings of the disablement process, sometimes termed ‘preclinical disability’ [Fried et al., 1996], because people compensate for their limitations by changing their activity pattern. Therefore, from LASA-C through LASA-G a branching question was added after each item to achieve greater sensitivity of the functional limitations questionnaire:

Do you do this activity less often than you would want or than is necessary?

Response categories: 1) no, 2) yes.

Again, this question was not asked of respondents who reported not being able to do the activity at all.

This question can also be interpreted as measuring avoidance of activities.

The branching questions on assistive devices, personal assistance, and avoidance each can be summed to a scale counting the yes-responses (see Appendix 2).

Questionnaires
LASAB030 / LASAC030 / LASAD030 /LASAE030 /LAS2B030 / LASAF030 / LASAG030 / LASAH030 / LAS3B030 / LASMB030 / LASAI030 /LASAJ030 / LASAK030 (main interview: in Dutch);
variables 401 – 412 in LASAC183 / LASAD183 / LASAE183 (medical interview, in Dutch);
LASAC603 / LASAD603 / LASAE603 / LASAF603 / LASAG603 / LASAH603 / LASAI603 / LASAJ603 / LASAK603 (telephone interview with PROXY, in Dutch)
LASAC703 / LASAD703 / LASAE703 / LASAF703 / LASAG703 / LASAH703 / LASAI703 / LASAJ703 / LASAK703 (telephone interview with RESP, in Dutch)

Interim Measurement:
LASEs803 (self-admin. questionnaire: in Dutch)
LASEt603 (telephone interview with PROXY, in Dutch)
LASEt703 (telephone interview with RESP, in Dutch)

Variable information
LASAB030 / LASAC030 / LASAD030 /LASAE030 /LAS2B030 / LASAF030 / LASAG030 / LASAH030 / LAS3B030 / LASMB030 / LASAI030 / LASAJ030 / LASAK030;
LASAB230 / LASAC230 / LASAD230 /LASAE230 /LAS2B230 / LASAF230 / LASAG230 / LASAH230 / LASA3B230 / LASMB230 / LASAI230 / LASAJ230 / LASAK230 (sumscores}
(pdf);
variables mlimshelf-mlimrun in LASAC183 / LASAD183 / LASAE183
(pdf);
LASAC603 / LASAD603 / LASAE603 / LASAF603 / LASAG603 / LASAH603 / LASAI603 / LASAJ603 / LASAK603
(pdf);
LASAC703 / LASAD703 / LASAE703 / LASAF703 / LASAG703 / LASAH703 / LASAI703 / LASAJ703 / LASAK703
(pdf)
Interim Measurement:
LASEs803; LASEs903 (sumscores)
(pdf);
LASEt603
(pdf);
LASEt703
(pdf)

Availability of information per wave ¹

	LSNa	B	C	D	E	IM*	2B*	F	G	H	3B*	MB*	I	J	K
Stairs	Ma 030	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Sa s803 s903	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230
			Tel 603 703	Tel 603 703	Tel 603 703	Tel t603 t703		Tel 603 703	Tel 603 703	Tel 603 703			Tel 603 703	Tel 603 703	Tel 603 703
Transport		Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Sa s803 s903	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230
			Tel 603 703	Tel 603 703	Tel 603 703	Tel t603 t703		Tel 603 703	Tel 603 703	Tel 603 703			Tel 603 703	Tel 603 703	Tel 603 703
Toenails		Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Sa s803 s903	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230
			Tel 603 703	Tel 603 703	Tel 603 703	Tel t603 t703		Tel 603 703	Tel 603 703	Tel 603 703			Tel 603 703	Tel 603 703	Tel 603 703
Dress	Ma 030		Ma 030 230	Ma 030 230	Ma 030 230	Sa s803 s903	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230
			Tel 603 703	Tel 603 703	Tel 603 703	Tel t603 t703		Tel 603 703	Tel 603 703	Tel 603 703			Tel 603 703	Tel 603 703	Tel 603 703
Chair	Ma 030		Ma 030 230	Ma 030 230	Ma 030 230	Sa s803 s903	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230
			Tel 603 703	Tel 603 703	Tel 603 703	Tel t603 t703		Tel 603 703	Tel 603 703	Tel 603 703			Tel 603 703	Tel 603 703	Tel 603 703
Walk	Ma 030		Ma 030 230	Ma 030 230	Ma 030 230	Sa s803 s903	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230
			Tel 603 703	Tel 603 703	Tel 603 703	Tel t603 t703		Tel 603 703	Tel 603 703	Tel 603 703			Tel 603 703	Tel 603 703	Tel 603 703
Shower/bath							Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230	Ma 030 230		Ma 030 230	Ma 030 230	Ma 030 230
Limitations in joint mobility			Me 183	Me 183	Me 183
	LSNa	B	C	D	E	IM*	2B*	F	G	H	3B*	MB*	I	J	K

¹ More information about the LASA data collection waves is available here.

* IM=interim measurement between E and F (first cohort only)
2B=baseline second cohort;
3B=baseline third cohort;
MB=migrants: baseline first cohort

Ma: data collected in main interview (LSNa030 / LASA030 / LASA230 for sumscores);
Me: data collected in medical interview (mlimshelf-mlimrun in LASAC183/LASAD183/LASAE183);
Sa: data collected in self-administered questionnaire (LASEs803);
Tel: data collected in telephone interview (LASA603 / LASA703)

Previous use in LASA
Functional limitations have been used in numerous LASA-studies, often as covariate, but also very often as an outcome measure. At the first LASA cycle, the association between functional limitations self-reports and performance tests was moderate (Spearman correlation: 0.48; partial correlation, with age partialed out: 0.42) [Deeg, 1994]. Analysis of reliable change in functional limitations (defined according to the Edwards-Nunnally criterion [Speer & Greenbaum, 1995] showed greater declines in older persons with lower socio-economic status as compared to higher socio-economic status [Broese van Groenou & Deeg 2000]. A prediction model of incident disability was shown to include age, handgrip strength, gait speed, five-repeated chair stands time, body mass index, cardiovascular disease, diabetes, chronic obstructive pulmonary disease, arthritis, and depressive symptoms [Jonkman et al 2019]. Combinations of somatic diseases had differential effects on functional decline [Kriegsman et al. 2004]. Functional limitations proved to be predictive of fractures, independent of physical performance [Stel et al 2004].

A study of the use of assistive devices showed that despite an increase in disability over three years, there was no change in self-rated health compared to age peers, except for a small improvement for respondents prolonging assistive device use [Boons et al 2016].

In a study of health trends over time, Galenkamp and colleagues [2013] showed that across 17 years, mild disability increased whereas severe disability decreased.

A review of LASA-based research on functional limitations and disability up to 2009 can be found in Deeg et al. [2009 and 2012].

References

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Date of last update: July 17, 2020