Xuxi Zhang

the Physical Component Summary (PCS) and Mental Component Summary (MCS), both ranging from 0 (lowest) to 100 (highest level of health). 23 Activity restriction was measured with the Groningen Activity Restriction Scale (GARS) which contains 18 items on independence of activities of daily living (GARS ‐ ADL; 11 items) and instrumental ADL (GARS ‐ IADL; 7 items). 24 The GARS score ranges from 18 (highest) to 72 (lowest level of independence) and the GARS–ADL score from 11 (highest) to 44 (lowest level of independence). Participants with a GARS score ≥ 29 were categorized as experiencing a loss of independence. 24 Mental well ‐ being was measured with the full 5 ‐ item mental well ‐ being scale of the 36 ‐ Item Short Form Survey (MHI ‐ 5) which measures nervousness, downheartedness and feeling sad, jollity, calmness and happiness (score range: 0 ‐ 100). 25, 26 Participants with a MHI ‐ 5 score ≤ 52 were categorized as showing signs of poor mental health. 25 Loneliness was measured with the short 6 ‐ item version of the De Jong Gierveld loneliness scale (short ‐ JG) which contains 2 domains: emotional (3 items) and social loneliness (3 items). 27 The overall loneliness score ranges from 0 ‐ 6 and the domain scores from 0 ‐ 3, with higher scores indicating a higher experience of loneliness. Participants with a short ‐ JG score ≥ 2 were categorized as feeling lonely. Physical frailty was additionally assessed with the Survey of Health, Ageing and Retirement in Europe ‐ Frailty Instrument (SHARE ‐ FI) which contains 5 items: exhaustion, weight loss, slowness, physical activity and hand ‐ grip strength. 28, 29 An estimation of a discrete factor model based on the 5 items determined whether participants were physically frail. 28 Activity limitation was measured with the 1 ‐ item Global Activity Limitation Index (GALI). Participants who indicated their function to be moderately or severely limited were categorised as having a limited function. 30, 31 Socio ‐ demographic factors Age (in years), sex, level of education, living situation (living alone/not living alone) were assessed. The level of education concerned the highest level of education the participant completed and was categorized according to the 2011 International Standard Classification of Education (ISCED) 32 into primary or less (ISCED 0 ‐ 1), secondary or equivalent (2 ‐ 5) and tertiary or higher (6 ‐ 8). Statistical Analyses Scale scores were described by conventional descriptive statistics. 33 We applied the framework used by Gobbens et al 7 who originally developed the TFI for the evaluation of the internal consistency and specific aspects of the validity of the TFI. The internal consistency was assessed with the Cronbach alpha; a value of the Cronbach alpha between 0.7 to 0.9 was considered as a satisfactory internal consistency. 34 To examine the convergent and divergent validity, we hypothesized that the SF ‐ 12 PCS, GARS and GARS ‐ ADL strongly relate to the 4 81 Reliability and validity of the TFI