Aim
The primary objective of this study was to assess the discriminative validity of the Core Outcome Set Functional Independence in a population of Dutch older adults (≥ 65 years of age) with different levels of functional independence. Because no gold standard exists for the assessment of FI that could be used to validate the newly developed Core Outcome Set, the level of FI was determined by whether older adults live independently without help, independently with help, or in a residential care facility. The secondary aim was to assess to what extent the domains ‘coping’, ‘empowerment’ and ‘health literacy’ contribute to the Core Outcome Set Functional Independence in addition to the domain ‘physical capacity’ in a population of Dutch older adults (≥ 65 years of age).
Study Design
This study was a cross-sectional validation study.
Population and setting
Participants were community-dwelling older adults as well as older adults, living in residential care facilities in the Netherlands. Data were collected from February until May 2019. Identification of eligible older adults was done by district nurses and physical therapists. Also, recruitment took place by inviting older adults to participate through local newspapers and social media. Older adults could be included if they were 65 years or over and were able to understand verbal and written instructions in Dutch. Older adults with severe cognitive impairments which hindered completing the questionnaires, were excluded.
Study procedure
Older adults were asked to come to a local test location or were offered a home visit to complete the measurements consisting of physical examinations and questionnaires. After giving written informed consent, they were guided through the approximately 60-minute test-procedure. Physical examinations were conducted by trained researchers and students with different (clinical) expertise and background, for example physical therapy, occupational therapy and human movement sciences. Participants could complete the questionnaires themselves but were offered help from a member of the research team when needed. The test-procedure included (1) the measurements of the Core Outcome Set FI, (2) measurement of a reference variable to validate the Core Outcome Set, and (3) a general questionnaire for demographic characteristics. The following section contains a description of the Core Outcome Set and the reference variable.
(1) Core Outcome Set Functional Independence
In the development process of this Core Outcome Set FI, recommendations from the Guideline for Selecting Outcome Measurement Instruments for Outcomes included in a Core Outcome Set were followed.4 The choice of specific measurement tools was determined by clinimetric properties of existing instruments representing the domains, their usability in the home-environment, availability in Dutch and multiple consensus meetings of the research group. Adjustments were made after pilot testing, based on the experiences of the researchers and the older adults who were tested.
The Core Outcome Set FI contains four domains:
Physical capacity
Physical capacity was defined as the composite of all the physical capacities a person can draw on (generally described in terms of body system functions such as strength, balance).5 Physical capacity was measured by four physical tests. The Short Physical Performance Battery (SPPB) is recommended to assess physical capacity in older adults.6,7 The SPPB consists of three subscales: balance, gait speed and lower extremity strength.6,7 To test static balance more extensively, the Frailty and Injuries Cooperative Studies of Intervention Techniques (FICSIT-study) measurement instrument FICSIT-4 was added to the SPPB. It measures the ability to maintain balance over a diminishing base of support.8 Because dynamic balance during walking is also an important component of physical capacity,9 the Timed Up and Go test (TUG) was added to the measurements. The TUG measures the time needed to stand up from a chair, walk three meters, turn, walk back and sit down. Furthermore, hand grip strength was measured three times for each hand with a JAMAR hand-held dynamometer, because this reflects overall muscle strength in older adults.10 The maximum value in kilograms was administered.11
Coping
For coping the Coping Flexibility questionnaire (COFLEX) was used, based on the following definition of the domain: Ability of the individual to use both assimilative and accommodative coping strategies to deal with stressors in different situations (versatility and reflective coping).12 While using assimilative coping strategies a person actively influences his or her situation to reach personal goals. With accommodative coping strategies personal goals are tailored to restrictions of a given situation. The versatility scale measures the ability to switch between assimilative and accommodative coping strategies, depending on personal goals and environmental circumstances. The reflective coping scale measures the ability to choose a coping strategy that fits the circumstances. This results in two scores, one for each aspect.
Empowerment
Empowerment was seen as the discovery and development of one’s inherent capacity to be responsible for one’s own life.13 People are empowered when they have sufficient knowledge to make rational decisions, sufficient control and resources to implement their decisions, and sufficient experience to evaluate the effectiveness of their decisions.13 The Patient Activation Measure (PAM) is recommended to measure the concept of empowerment.14 The PAM-13 consists of thirteen statements on a four-point Likert scale and results in four levels of patient activation.15
Health literacy
Health literacy was defined as people’s knowledge, motivation and competences to access, understand, appraise and apply health information.16 This enables them to make judgements and take decisions in everyday life concerning healthcare, disease prevention and health promotion to maintain or improve quality of life during the life course. The Newest Vital Sign (NVS-D) is a six-question tool to assess one’s level of health literacy by determining an individual’s ability to find and interpret information on an ice-cream nutrition label.17
Clinimetric properties of the included measurement instruments are described in table 1.
Table 1: Clinimetric properties Core Outcome Set Functional Independence
Domain
|
Instrument
|
Target population
|
Clinimetric properties
|
Physical capacity
|
SPPB
|
Older adults6
|
Predictive for developing disability and identifies subgroups who have high and low risk of disability (AUC .75).6,18 Cut-off points are scores of four and nine.19 Good intrarater reliability (ICC .88 - .92) and high construct and concurrent validity.6
|
|
FICSIT-4
|
Older adults8
|
Moderate to good reliability (Interclass Pearson correlations .25 to .74).8 Good concurrent validity.8
|
|
TUG
|
People with hip and knee osteoarthritis, patients with stroke and older adults with dementia20,21
|
Good reliability (ICC .75 to .99).20,21 Good construct and convergent validity.20,22 The cut-off point for independent walking is 20 seconds.23When it is impossible to complete the TUG, a fictive score of 240 seconds is registered.23
|
|
JAMAR
|
General population and community-dwelling older adults24,25
|
Excellent intra- and interrater reliability (ICC .98 and .94).24 Good test-retest reliability (ICC .91 for right and .95 for left hand).25 MCID is 6.5 kilogram.26
|
Coping
|
COFLEX
|
Patients with chronic reumatoïd arthritis12
|
Acceptable internal consistency (Crohnbach’s α of respectively .88 and .70 for the subscales).12Construct validity good for the versatility scale.12
|
Empowerment
|
PAM-13
|
Older adults and older adults with multimorbidity
|
Good internal consistency (Crohnbach’s α of .88).15,27 Good construct validity.27,28
|
Health literacy
|
NVS-D
|
Older adults
|
Good internal consistency (Chronbach’s α of .76).17Cut-off point between adequate and inadequate health literacy is a score of four or more.17
|
SPPB = Short Physical Performance Battery; FICSIT = Frailty and Injuries Cooperative Studies of Intervention Techniques; TUG = Timed Up and Go test; COFLEX = Coping Flexibility questionnaire; PAM = Patient Activation Measure; NVS-D = Dutch Newest Vital Sign; AUC = Area Under the Curve; ICC = Intraclass Correlation Coefficient; MCID = Minimal Clinically Important Difference
(2) Reference Variable
To validate the Core Outcome Set FI a reference variable was used. Because no gold standard for FI exists, a proxy indicator was composed based on two conditions.
First, the definition of FI includes ‘independent from another person’, so help needed in (instrumental) activities of daily living ((i)ADL) was included in the proxy indicator. This was determined based on the Groningen Activity Restriction Scale (GARS-3), since GARS-3 showed adequate discriminative validity in a population of older adults.29 This eighteen item questionnaire gives an indication of disabilities in the domains of personal care and domestic activities by registering if a person can do activities in three categories: with no effort (score one), with effort (score two) or only with help of others (score three).29 When people score three on one or more of the items, they need some kind of help with personal care or domestic activities.
Second, as the definition of FI includes ‘functioning physically safe, within the own context’, living situation was part of the proxy indicator. A difference was expected in level of FI between people living independently and people living in a residential care facility. The main reason for admission to a residential care facility is the presence of substantial limitations in activities of daily living.1 These are influenced by multi-morbidity, physical impairments, a low sense of self-management, and diminished social support.1 A substantial part of this influencing factors is related to the concept of FI.
This combination of help needed in (i)ADL and living situation results in three levels of (impairments in) FI. These are described in figure 1.
Statistical analyses
Descriptive statistical analyses were conducted on participant’s age, gender, educational level, presence of morbidities and type of residence. Demographic characteristics and scores on the Core Outcome Set were calculated by mean and standard deviation or median and interquartile range for continuous variables and proportions for categorical variables. Differences between groups were calculated by One-way ANOVA for normally distributed continuous variables, Kruskal-Wallis for not normally distributed variables and Chi-square test for categorical variables.
To determine discriminative validity of the Core Outcome Set FI, reflected by the ability of the Core Outcome Set to predict the level of FI for three different subgroups, ordinal logistic regression was performed. First, the assumptions for logistic regression were tested. After that a model was built with group membership as dependent variable. All scores of the Core Outcome Set FI were entered as predictor variables in the ordinal regression model using ‘forced entry terms’. Based on the rule of thumb of ten events per variable for logistic regression analysis and eight included variables, a sample size of a minimum of 80 people in each group was optimal.30
To meet the second objective of the study, likelihood statistics of subsequently a null-model, a model with only physical capacity and models with physical capacity and respectively (combinations of) coping, empowerment or health literacy were tested for improvement of the model using a likelihood ratio (LR) test (X2 test). P-value <0.05 was considered significant. When missing values occurred in the dependent or one of the predictor variables, these cases were excluded from the analysis.
Statistical analyses were performed using IBM Statistical Package for the Social Sciences (SPSS, version 24,0 Armork, New York, USA).