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. 2016 Oct 19;11(10):e0165127. doi: 10.1371/journal.pone.0165127

Table 2. Synthesis of risk and protective factors for developing limitations in ADLs with combined strength of evidence per factor.

Domain Specific factor(s)* (reference category if not the direct opposite) Number of studies** (n risk, protective, indefinite, NSA) Interpretation*** Combined strength of evidence****
Socio-demographic characteristics
Age Higher baseline age 7 (5,0,2,0) Risk +++
Ethnicity / race

  • African Americans / Hispanic Americans (Non-Hispanic whites)

  • Non-Hispanic other / black / Hispanic (Hispanic white)

  • Minor ethnicity

  • Black (white)

 4 (0,0,4,0) Protective (subgroups) +
Gender Female gender 5 (4,0,1,0) Risk ++
Household composition Living alone 5 (0,0,2,3) Unclear
Living with spouse / children / spouse and children / others 1 (0,0,1,0) Risk +/-
Living environment

  • Glostrup / Yyväskylä (Göteburg)

  • Glostrup (Yyväskylä)

  • Urban (rural)

  • (Sub)urban (hilly)

  • Midwest / Northeast / West (South, USA)

  • Rural (urban)

 6 (0,1,2,3) Protective (rural) Risk (urban, Midwest; subgroups) +/-
Marital status Being married 4 (0,2,1,1) Protective +
Being divorced/separated/widowed, and never married 1 (0,0,0,1) NSA +/-
Place of birth Midwest / South / West / outside US (Northwest) 1 (0,0,1,0) NSA +/-
Socio-economic characteristics
Education Own education:

  • ≤ 11 years

  • ≤ 8 years

  • 9–11 years (>high school)

  • Education

  • Years of education

 4 (1,0,2,1) Risk (not fully-adjusted) ++
<8 years of mother’s education 1 (0,0,1,0) Risk (not fully-adjusted) +/-
Housing tenure Not owning a house 1 (0,0,0,1) NSA +
Income/wealth Lower income/wealth levels 1 (1,0,0,0) Risk +/-
Having financial resources 2 (0,0,1,1) Unclear
Occupation

  • Operators, craftsmen, farmers / clerical and service industry workers / never worked / no lifetime occupation (white-collar)

  • Being a veteran

  • Non-agriculture / housewife (agriculture)

 2 (0,0,1,0) Risk +
Socioeconomic status as a child Poor/varied SES as child (well off/about average) 1 (0,0,1,0) Risk (not fully-adjusted) +/-
Psychosocial factors
Loneliness Feeling lonely 1 (0,0,0,1) NSA +/-
Social participation

  • Diversity in social relations

  • Membership in club for retired people

  • Paying and receiving visits, participating outside the home

  • Not helping others, i.e. taking care of others, sewing, and make repairs

  • Having weekly telephone contact with children

  • Not going out at least once a week

 3 (0,0,1,2) NSA Risk (sewing) +
Receiving formal support Receiving support 1 (0,0,0,1) NSA +/-
Receiving informal support Receiving support 1 (0,0,0,1) NSA +
Self-reported conditions
Anxiety 1 (0,0,0,1) NSA +
Arthritis 2 (1,0,0,1) NSA +
Cancer 1 (1,0,0,0) Risk +/-
Depression 1 (0,0,0,1) NSA +
Diabetes 2 (2,0,0,0) Risk +
Eye disorder 1 (0,0,1,0) Unadjusted risk +
Fractures 2 (0,0,0,2) NSA ++
Heart disease 3 (1,0,0,2) NSA ++
Hypertension 3 (2,0,0,1) Unclear
Lung disease 2 (1,0,0,1) NSA +
Number of chronic diseases

  • 0 versus 1 versus 2–8

  • 0–13

 2 (0,0,0,2) NSA ++
Psychiatric disorder 1 (1,0,0,0) Risk +/-
Stroke 2 (2,0,0,0) Risk +
Health behaviour
Alcohol consumption Currently drinking alcohol 1 (0,0,0,1) NSA +/-
Physical activity

  • Performing activities weekly

  • ≥ 2 / <2 hours (no activity)

  • Hours a week4 hours / vigorous sports ≥ twice weekly (<4 hours)

  • Involvement in activities

  • Involved in physical exercise program

 5 (0,4,1,0) Protective +++
Smoking Not smoking 1 (0,1,0,0) Protective +/-
Quitted smoking (never) 1 (0,0,0,1) NSA +/-
Smoking (never) 1 (1,0,0,0) Risk +/-
Observed health-related measures
Cognition

  • Digit span and -symbol, fluency, visual reproduction, Raven’s progressive matrices

  • Errors on modified SPMSQ

  • (Modified) MMSE

 4 (1,0,0,3) NSA ++
Depression

  • CES-D

  • GDS

  • Depression risk

 3 (0,0,1,2) NSA ++
Blood pressure No hypertension 1 (1,0,0,0) Risk +
Higher diastolic blood pressure (DBP) 1 (0,0,0,1) NSA +/-
Higher mean arterial pressure (MAP) 1 (0,1,0,0) Protective +/-
Higher pulse pressure (PP) 1 (0,1,0,0) Protective +/-
Higher systolic blood pressure (SBP) 1 (0,1,0,0) Protective +/-
Frailty ≥ 2 affected frailty domains 1 (1,0,0,0) Risk +/-
In need of long-term care Based on physical strength, nutritional status, oral function, houseboundness, cognition, and depression risk 1 (0,0,0,1) NSA +/-
Limitations in IADLs ≥ 1 out of 7 activities 1 (0,0,1,0) Unadjusted risk +
Limitation in gait/balance 1 (1,0,0,0) Risk +
Limited muscle strength Low grip strength 2 (1,0,0,1) Unclear
Low elbow flexion strength 1 (1,0,0,0) Risk +
Low knee extension strength 1 (1,0,0,0) Risk +
Low trunk extension strength 1 (0,0,0,1) NSA +
Low trunk flexion strength 1 (1,0,0,0) Risk +
Number of chronic diseases 2–7 (0–1) 2 (1,0,1,0) Unadjusted risk +
Other physical function limitation
Poor functional reach 1 (0,0,1,0) Risk (not fully-adjusted) +
Poor physical strength 1 (0,0,0,1) NSA +/-
Low manual dexterity 1 (1,0,0,0) Risk +
Step climbing 1 (0,0,1,0) Risk (not fully-adjusted) +
Tiredness in activities 1 (0,0,1,0) Risk +
Low walking speed 1 (1,0,0,0) Risk +
Weight
Weight gain 1 (1,0,0,0) Risk +
Weight loss 1 (0,0,1,0) Unadjusted risk +
Vitamin status
25(OH)D vitamin status: ng/ML <20.0 / 20.0–29.9 1 (0,0,0,1) NSA +/-
Self-reported health-related measure
Falls 1 (0,0,0,1) NSA +/-
Cognition Question-based (e.g. “do others point you to forgetfulness?) 1 (0,0,0,1) NSA +/-
Hearing Good / fair/poor hearing (excellent/very good) 1 (0,0,1,0) Risk +/-
Medication High medication use 1 (0,0,0,1) NSA +
Pain Experiencing daily / multiple site / moderate to severe pain (no pain) 1 (0,0,1,0) Risk +
Peak stature Based on self-reported height 1 (0,0,1,0) Risk (not fully-adjusted) +/-
Self-rated health Fair/poor / good / very good (excellent) 4 (0,0,2,2) Unclear
Self-rated health as a child (recalled) Fair/poor / good / very good (excellent) 1 (0,0,1,0) Risk +/-
Subjective well-being E.g. quality of life and happiness 1 (0,0,0,1) NSA +/-
Vision

  • Impaired vision

  • Vision less than excellent/very good

 2 (1,0,1,0) Risk +/-
Weight / nutrition Obesity (BMI ≥ 30) 1 (1,0,0,0) Risk +/-
Weight loss

  • Unintentional

  • BMI

  • Anorexia of ageing

 3 (0,0,2,1) Unclear
Other
Proxy response 1 (1,0,0,0) Risk +/-

* Underlined: statistical significant risk or protective factor (in case multiple categories were examined / instruments were used)

** Risk = statistical significant increased risk for developing limitations in ADLs; Protective = statistical significant decreased risk for developing limitations in ADLs; Indefinite = findings differ per model, and/or per subgroup (e.g. Gu & Yi [29] reported findings per age group and by gender); NSA = no statistically significant association

*** Unclear = different findings across studies; NSA = highest combined strength of evidence for studies that did not found statistically significant associations

**** +++ = evidence in ≥ 3 high quality studies; ++ = evidence in 2 high / ≥3 low quality studies; + = evidence in 1 high / 2 low quality studies; +/- = evidence in 1 low quality study