A cross-sectional study was conducted among community-dwelling older people in Limburg, a province in the southern part of The Netherlands. The medical ethical committee Atrium-Orbis-Zuyd approved this study (12-N-129). Selection of the study population was made from the Health Monitor, an extensive postal general health questionnaire which is sent every four years by the Community Health Service to a large sample of community-dwelling people in the Netherlands [15].
Study population
For the measurement using the Health Monitor in Limburg, during the fall of 2012, 56,000 people aged 55 years and over were selected. Selection was random for all age groups, except for those over 75 years. This population was overrepresented in the sample in order to obtain sufficient data among the oldest age group living at home. People living in neighbourhoods with a low socioeconomic status were overrepresented as well. Respondents were asked to give their consent for using their data for our study.
The response rate for the Health Monitor was 54 % (n = 30,130). Of the respondents, 13,521 gave permission for the use of their data in our study. The selection was also restricted to those who were 65 years and older, because this is the age group in which the Fried criteria were originally developed [5]. After excluding the questionnaires that were filled out by a person other than the addressee and those questionnaires with a significant amount of missing data, a total of 8,684 people participated in our study.
Measurements
The Health Monitor is comprised of a broad range of questions. In addition to demographic characteristics (age, gender, marital status and level of education), questions included the Fried frailty criteria, (chronic) diseases, use of healthcare services, use of informal care and items about social, psychological and physical functioning.
Fried frailty criteria
Fried and colleagues developed five criteria (weight loss, exhaustion, low physical activity, slowness and weakness) to be used for identifying frail older people [5]. In contrast with the original criteria, we replaced the two physical measurements of slowness and weakness by questions. Weight loss was measured using the question: “In the last year, have you lost more than 4.5 kilograms unintentionally? (i.e. not due to dieting or exercise)”. This question is the same as proposed by Fried and colleagues, only pounds were replaced by kilograms. This criterion was met when the participant answered “yes”. Exhaustion was measured using two questions from the Center for Epidemiologic Studies Depression (CES-D) scale: “How often did you feel that everything you did was an effort?” and “How often did you feel that you could not get going?” [16, 17]. These questions are the same as proposed by Fried and colleagues. Response options were slightly different: “always, most of the times, sometimes, occasionally, never”, compared to “rarely or none of the time (<1 day), some or a little of the time (1–2 days), a moderate amount of the time (3–4 days), most of the time” in Fried’s version. This criterion was met when participants answered: “always or most of the times” to at least one of the two questions. Low physical activity was not measured by using the Minnesota Leisure Time Activity Questionnaire, as proposed by Fried and colleagues. Instead, a slightly adjusted version of the Short Questionnaire to Assess Health-enhancing physical activity (SQUASH) was used [18]. Participants had to answer questions about how many times a week they spent time walking, cycling, gardening, doing odd jobs or exercising/playing sports. For each activity, they had to report how much time they spent engaged in that activity on each occasion. Kilocalories per week were calculated. The results were stratified by gender and compared with the cut-off values as described by Fried and colleagues (men 383 kcal/week, women 270 kcal/week). If a person used fewer kcals per week this criterion was met. Slowness/walk time was measured using the question: “Can you reach the other side of the road when the light turns green at a zebra crossing?” We developed this question ourselves. If the participant chose any reply other than “yes, without any trouble”, the criterion was met. Weakness/grip strength was measured by asking the question: “Do you experience difficulties in daily life because of low grip strength?” This question was derived from the Tilburg Frailty Indicator [8]. If the participant answered “yes”, the criterion was met.
The stages of frailty, based on the Fried criteria, were defined as follows: a score of 0 means that a person is robust or not frail. Persons with a score of 1 or 2 are at intermediate risk for adverse outcomes or are considered to be pre-frail. A score of 3–5 indicates that someone is frail [5].
Perceived health and healthcare use
One question was asked regarding perceived health: “How well is your health in general?” The question could be answered on a 5-point Likert scale with answer choices ranging from “very good” to “very poor”. The use of healthcare services was measured by reporting any contact with a general practitioner within the last two months. The participants also had to provide details regarding the healthcare professional they had contacted over the past twelve months. The healthcare providers were already specified: medical specialist, dietician, occupational therapist, physiotherapist, homecare (nursing care and household care) and social worker.
Social domain
Wenger and colleagues developed an 8-item questionnaire regarding social network [19]. The scores divided people into five types of support networks: family dependent, locally integrated, local self-contained, wider community focused, and private restricted. The family dependent and private restricted support networks are characterised by a limited number of people that could provide support. The locally integrated and wider community-focused support networks are larger networks. Wenger and colleagues found that these network types were consistent with the availability of informal support and the use of healthcare services [19]. In addition, one question was asked about the use of informal care over the past 12 months. Loneliness was measured by using the De Jong-Gierveld Loneliness Scale [20]. This is an 11-item scale, with questions such as “I miss having a really close friend”, which allows the participants to choose from three answer choices: “yes”, “more or less” or “no”. A higher score indicates more feelings of loneliness.
Psychological domain
The 10-item Kessler Psychological Distress Scale (K-10) was used to measure psychological distress [21]. This questionnaire is comprised of questions such as: “During the last four weeks, about how often did you feel depressed?” The five-category response scale ranged from “all of the time” (score 5) to “never” (score 1). A higher total score indicated higher levels of psychological distress. Mastery was assessed by using Pearlin and Schooler’s instrument [22]. Seven statements, such as: “I have little control over the things that happen to me”, are answered using a 5-point scale, ranging from “I totally agree” to “I totally disagree”. The higher the total score, the more the respondent thinks that life-chances are under one’s own control. Self-management was measured using the short version of the Self-Management Ability Scale (SMAS-S) [23]. The SMAS-S consists of six three-item subscales (taking initiative, investment behaviour, variety, multifunctionality, self-efficacy and positive frame of mind), which reflect core abilities to form the construct of self-management of well-being [24]. Response options were slightly adjusted so that every question had six possible answers. Therefore, the final scores range from 1 to 6, with a higher score indicating more self-management abilities.
Physical domain
Chronic diseases were measured by asking participants whether or not they suffered from one or more of the following chronic diseases: diabetes, stroke/cerebral haemorrhage/cerebral infarction, myocardial infarction, other cardiac diseases, cancer, asthma, chronic obstructive pulmonary disease (COPD), hip or knee arthrosis, chronic joint inflammation, or back problems (incl. hernia). For cancer and myocardial infarction the participants had to report if they ever had the diseases. For all of the other diseases, they had to report whether they suffered from the disease over the past twelve months.
IADL-disability (Instrumental activities of daily living) was measured using a seven-item subscale from the Groningen Activity Restriction Scale (GARS) [25, 26]. The subscale is comprised of questions, such as “Can you fully independently prepare dinner?” The items were answered on a four-point scale, with answers ranging from “Yes, without any difficulty” to “No, only with someone’s help”. Scores range from 7 to 28 points, with a higher score indicating a higher level of IADL-disability. Physical limitations were assessed using the Organization for Economic Cooperation and Development (OECD) long-term disability questionnaire [27]. In this study, we used a six-item version, as used by the Community Health Service. This version is comprised of questions about problems with hearing, vision, bending, and walking 400 metres. The number of items that people indicated as problematic were used for analysis.
Statistical analysis
The central focus of this study was to describe the levels of functioning across various domains. Descriptive statistics were used to present demographic characteristics of the study population and the levels of functioning. Associations between scores in the three health domains and the frailty stages were analysed using Kendall’s tau for nominal and ordinal variables, and analyses of variance (ANOVA) for all other variables (P < 0.05).These associations were also studied separately for men and women, as older women are more likely to be frail. Where available, missing data for all of the included instruments were handled as proposed by the original authors. Fried and colleagues excluded people with three or more missing frailty components. Missing data with respect to the Fried criteria in our study were handled more strictly than originally proposed by the authors. To reduce the number of misclassifications, only one missing value was allowed when a person had a valid Fried score of 0–2. If a person had a valid Fried score of 3 points or more, two missing values were allowed, because this would not cause misclassification. The analyses were performed using IBM SPSS Statistics software version 19.