Other measurements
Health-related and sociodemographic characteristics are assessed via the patient questionnaires and administrative data from the individual pension insurance account. Both groups receive a two-page questionnaire. These variables are collected for sample description, group comparison and to identify relevant covariates related to application for prevention or rehabilitation services. The intervention group additionally completes the two-page ”screening 45+”.
Dimension A - work ability
Work ability is assessed by adapted questions from the "Screening Instrument to Assess the Need for Medically and Occupationally Oriented Measures" (SIMBO) and the "Work Ability Index" (WAI). The SIMBO has already been used in numerous studies (39, 40). The question on sick leave in the past 12 months with the 5-point scale (0 "not at all" to 4 "more than 6 months") and on the expected future work ability with a 4-point scale (0 "no severe health impairment" to 3 "no longer working at all") were included in a modified form. The WAI is a questionnaire that can provide conclusions about employees' ability to work in relation to their individual conditions and the underlying working conditions (41–43). In the "screening 45+", the question on the self-rated work ability was adapted with a 6-point scale (0 "no impairment" to 5 "can no longer work at all").
Dimension B - mental well-being
Mental well-being is assessed via the short form of the Patient Health Questionnaire-4 (PHQ-4). The PHQ-4 is an ultra-short screening instrument with four items to identify depressive and anxiety symptoms (44). The items are rated on a 4-point scale from 0 ("not at all") to 3 ("almost every day"). The PHQ-4 is included in the "screening 45+" in an unmodified form.
Dimension C - functional ability
Functional ability is assessed via adapted questions from the generic questionnaire "Indicators of Rehab Status, Version 3" (IRES-3) (45). Four items were selected from the original scale. In comparison to the original version, the 5-point Likert scale was reduced to four levels for reasons of comparability with the items of the other dimensions. The central answer category was deleted. The level of activity can be documented from 0 ("no problem") to 3 ("impossible").
Dimension D - coping behaviour
The German Pension Insurance developed its own instrument consisting of four items to assess coping behaviour (37). Coping is measured in different domains on a 4-point Likert scale (0 "very good" to 3 "not at all").
Dimension E - physical activity
The items on physical activity are adapted from the National Health Service's “German Practice Physical Activity Questionnaire” (GPPAQ). The GPPAQ is a short self-report questionnaire that can be used to measure physical performance (46, 47). Four items were selected for the "screening 45+" and translated into German. In each case, the amount of time activity per week is recorded in different areas with four gradations from 0 ("2h or more") to 3 ("not at all").
Short questionnaire and administrative data
Subjective health status
The subjective health status is assessed, according to a recommendation of the World Health Organization (WHO) (48). There are five answer options from 0 ("very good") to 4 ("very poor"). This item is part of the Minimum European Health Module (MEHM) (49) and is applied in GEDA – German Health Update (50).
Previous use of rehabilitation services
The previous use of rehabilitation services may influence application behaviour (51); therefore the questionnaire asks whether a rehabilitation has already been carried out.
Further measurements of work ability
In the short questionnaire the current work ability compared with the lifetime best is measured by the “Work Ability Score” (WAS) (52), the first item from the WAI. The 11-point scale ranges from 0 ("completely unable to work") to 10 ("maximum ability to work"). The subjective prognosis of work ability is assessed with the SPE scale ("subjective prognosis of employability") (27). Considering the current state of health and work ability, the survey determines whether the current occupation can be carried out until retirement age (0 “sure” to 4 “definitely not”), whether the general work ability is permanently at risk and whether the person is currently considering applying for a disability pension.
Work-related data
The German Pension Insurance provides information on voluntary contributions on days with creditable periods due to unemployment in months and the occupational status.
Sociodemographic data
Further data regarding gender, age, educational and professional qualifications, subjective socio-economic status as well as primary language spoken in the household will be assessed via the short questionnaire.
Sample size estimation
The calculation of the sample size is based on a research project that evaluated the psychometric properties, reliability and criterion validity of the “screening 45+” (37). This study revealed a prevalence of 15.8% in total of persons needing prevention or rehabilitation services among insured persons of the German Pension Insurance aged 45 to 60 (n = 4,903): 13.0% showed a need for a prevention service and 2.8% a need for a rehabilitation service. Only a few of the persons with a need for prevention or rehabilitation services intend to submit an application. Moog et al. (11) estimate this proportion at 20%. Thus, we expect 3.2% of the participants in the intervention group to apply for a prevention or rehabilitation service after participation in the "check-up 45+". We assume an association between the "check-up 45+" and the application for a German Pension Insurance service if this takes place within 2 months. For the control group, we calculated the proportion based on the statistics from the German Pension Insurance (54). Consequently, the proportion of insured persons aged 45 to 59 who submit an application for prevention or medical rehabilitation services within two months is estimated at 0.73%.
In order to detect a difference between the intervention and the control group of applications for prevention and medical rehabilitation services, the power calculation (two-sided test, type I error rate: 5%, power: 85%) resulted in a required minimum sample size of n = 661 per group. We assume that a proportion of participants cannot be included into the analyses because they do not meet the inclusion criteria. Some inclusion criteria are difficult for the practice staff to verify when recruiting participants, e.g. insurance status. To take into account a possible drop-out rate of 20%, the targeted sample size is increased to n = 827 per group.
Recruitment
Before the recruitment phase, the study team visits the GP practices for a one-hour training session on the procedure of the study. The practice staff invite patients who visit the practice for standard care and meet the inclusion criteria (age, insured status) to participate in the study. Study information, consent form and questionnaires are handed out in envelopes for completion. To avoid selection bias, the practice staff is encouraged to address patients who fulfil the inclusion criteria, regardless of their health status and known need for rehabilitation. They should be approached in a neutral way without receiving information about potential prevention or rehabilitation services.
Allocation
Block randomisation will be performed for each general practice, with the same number of patients per block. Allocation to the intervention or control group is randomised within each block (10 blocks of 10 per practice) to keep the number of case IDs balanced, even if the lists are not finished. The case IDs were generated with R version 4.2.2 and are reproducible. Only the German Pension Insurance is able to link the pseudonyms to the actual persons.
The assignment of the participants included in the study to the intervention or control group is performed randomly, as the practice staff cannot influence the group affiliation of the invited participants during the recruitment process. The practice staff hand out the questionnaires and study documents in sealed, non-transparent envelopes on which the group affiliation is not indicated. The envelopes are only labelled with the questionnaire number (case ID) and are first opened by the participants.
Blinding
The practice staff are blinded during the recruitment process while inviting patients to the study. Once patients return the completed questionnaires, the practice staff are no longer blinded.
The patients are not aware of their group assignment, as they have no knowledge of the existence of two groups. Unblinding the control group is not intended. Participants in the intervention group are aware of the intervention when they are informed about the result of the "check-up 45+" after evaluation of the "screening 45+". The project coordinators at the German Pension Insurance have no knowledge of the group assignment. The Charité study staff who perform the analyses know the group assignment.
Data collection
Primary and secondary outcomes are provided by the German Pension Insurance registers and the questionnaire “screening 45+” (Table 3). Administrative data can be collected reliably and validly for both groups. The German Pension Insurance transmits these data electronically, encrypted and pseudonymised. This enables a complete recording of the administrative data of all study participants. The data collection by patient questionnaires takes place in the GP practices. The study procedure and the questionnaires were tested and adapted in advance in a pre-test with two practices. The practices start at staggered intervals and aim to recruit about 80 participants per practice. Completed questionnaires are stored in the GP practices. During recruitment, Charité study staff regularly visit GP practices to monitor procedures and collect patient questionnaires. Consent forms and study list are sent by the practices to the German Pension Insurance. If participants withdraw their consent, their collected data will be deleted.
After recruitment is completed, semi-structured interviews will be conducted by telephone or in person to investigate practicability and acceptance of the “check-up 45+”. Practice staff, participating patients and employees of the German Pension Insurance involved in the study will be interviewed. The interviews are recorded, transcribed, and analysed anonymously.