Table 3.
Summary table of direction and strength of evidence for each outcome, and strength of potential moderators and mediators
| Coding of outcome | Outcome | Vote counting | Strength of evidence (vote counting, magnitude of effect indicated by included meta-analyses, overall judgement) | Moderators (amplifying effect) and mediators |
|---|---|---|---|---|
| General | Health outcomes overall | N/A | N/A |
Moderators Structured reflection (use of) Age (older) SES (lower) Motivation (altruistic/intrinsic, religious) Social benefits (social connection, support and interaction) Optimal frequency (uncertain) Formality (uncertain) |
| Well-being (general) | 3 reviews with 7 unique studies were identified. All studies supported a positive effect, which was statistically significant (7/7; 100%, p = .016) | Moderate (consistent, magnitude of effect is small to very small) |
Moderators Formality (informal/mixed volunteering) Motivations (prosocial) Recipient response (feeling appreciated) Level of participation (organisational level) Frequency (mostly consistent) Mediators Religiosity (partial) |
|
| Quality of life | 7 reviews with 15 unique studies were identified. A statistically significant majority of studies supported a positive effect (13/15; 87%, p = .007) | Moderate (consistent, meta-analysis required to determine magnitude) |
Moderators Recipient response (feeling appreciated) Mediators Feeling appreciated |
|
| Psychological | Burnout and emotional exhaustion | 3 reviews with 12 unique studies were identified. A statistically significant majority of studies supported a positive effect (11/12; 92%, p = .006) | Moderate (consistent specifically within emotionally demanding roles, meta-analysis required to determine magnitude of effect) | Moderators Age (younger) Role (emotionally demanding) Positive coping strategies (lack of) Social support (lack of) Education (lower) Empathy with recipient (empathising) |
| Purposefulness and meaningfulness | 6 reviews with 9 unique studies were identified. All studies supported a positive effect, which was statistically significant (9/9; 100%, p = .004) | Moderate (consistent, meta-analysis required to determine magnitude) | ||
| Life satisfaction | 11 reviews with 30 unique studies were identified. A statistically significant majority of studies supported a positive effect (27/30; 90%, p < .001) | Strong (highly consistent, magnitude of effect is small) |
Moderators Formality (formal volunteering) Recipient response (feeling appreciated) Mediators Social benefits |
|
| Depression | 11 reviews with 41 unique studies were identified. A statistically significant majority of studies supported a positive effect (39/41; 95%, p < .001) | Strong (highly consistent, magnitude of effect is very small) | Moderators Recipient response (feeling appreciated) Gender (women) Age (older) Empathetic arousal (low) | |
| Psychological well-being | 10 reviews with 29 unique studies were identified. All studies supported a positive effect, which was statistically significant (29/29; 100%, p < .001) | Strong (highly consistent, meta-analysis required to determine magnitude) | ||
| Self-efficacy, self-esteem, and pride and empowerment | 12 reviews with 43 unique studies were identified. A statistically significant majority of studies supported a positive effect (40/43; 93%, p < .001) | Strong (highly consistent, meta-analysis required to determine magnitude) | Moderators (pride and empowerment) SES (lower) | |
| Positive affect | 7 reviews with 18 unique studies were identified. A statistically significant majority of studies supported a positive effect (16/18; 89%, p = .001) | Moderate (consistent, meta-analysis required to determine magnitude) | ||
| Motivation | 2 reviews with 5 unique studies were identified. All studies supported a positive effect, although non-significant (5/5; 100%, p = .063) | Weak (insufficient evidence, meta-analysis required to determine magnitude) | ||
| Anxiety | 3 reviews with 3 unique studies were identified. All studies supported a positive effect, although non-significant (3/3; 100%, p = .250) | Weak (insufficient evidence, meta-analysis required to determine magnitude of effect) | ||
| Mental health (general) | 2 reviews with 5 unique studies were identified. Findings were inconsistent (3/5; 60%, p = 1.00) | Very weak (inconsistent/mixed, meta-analysis required to determine magnitude) | ||
| Physical | Mortality | 8 reviews with 30 unique studies were identified. All studies supported a positive effect, which was statistically significant (30/30; 100%, p < .001) | Very strong (highly consistent, effect was the second largest outcome in magnitude of the meta-analyses included) |
Moderators Covariates (SES, age, religious attendance, social support and health habits) |
| Maintenance of functional independence and reduced functional disability | 7 reviews with 22 unique studies were identified. All studies supported a positive effect, which was statistically significant (22/22; 100%, p < .001) | Very strong (highly consistent, effects were the largest outcome in magnitude of the meta-analyses included) | ||
| Physical activity | 7 reviews with 16 unique studies were identified. All studies supported a positive effect, which was statistically significant (16/16; 100%, p < .001) | Strong (highly consistent, meta-analysis required to determine magnitude of effect) | ||
| Self-reported health | 10 reviews with 21 unique studies were identified. A statistically significant majority of studies supported a positive effect (18/21; 86%, p = .001) | Moderate (consistent, magnitude of effect is very small) |
Moderators Type (environmental compared to civic) Frequency (mostly consistent) |
|
| Grip strength | 3 reviews with 3 unique studies were identified. All studies supported a positive effect, although non-significant (3/3; 100%, p = .250) | Weak (insufficient evidence, meta-analysis required to determine magnitude of effect) | ||
| Decreased smoking | 1 review with 4 unique studies were identified. All studies supported a positive effect, although non-significant (4/4; 100%, p = .125) | Weak (insufficient evidence, meta-analysis required to determine magnitude of effect) | ||
| Blood pressure | 1 review reported one study (1/1; 100%) | Weak (insufficient evidence, requires more research) | ||
| BMI | Weak (insufficient evidence, requires more research) | |||
| Frailty | Weak (insufficient evidence, requires more research) | |||
| Living in a nursing home | 1 review reported one study (1/1; 100%) | Weak (insufficient evidence, requires more research) | ||
| Number of medical conditions | 1 review reported one study (1/1; 100%) | Weak (insufficient evidence, requires more research) | ||
| Social | Social network/ support | 5 reviews with 12 unique studies were identified. A statistically significant majority of studies supported a positive effect (11/12; 92%, p = .006) | Moderate (consistent, meta-analysis required to determine magnitude of effect) | |
| Social connectedness/ sense of community | 5 reviews with 18 unique studies were identified. A statistically significant majority of studies supported a positive effect (17/18; 94%, p < .001) | Strong (highly consistent, meta-analysis required to determine magnitude of effect) | ||
| Social integration | 2 reviews with 7 unique studies were identified. A majority of studies supported a positive effect, although non-significant (6/7; 86%, p = .125) | Weak (insufficient evidence, meta-analysis required to determine magnitude of effect) | ||
| General social benefits | 1 review with 2 unique studies were identified. All studies supported a positive effect, although non-significant (2/2; 100%, p = .500) | Weak (insufficient evidence, requires more research) | ||
| Social ties | 4 review with 4 unique studies were identified. All studies supported a positive effect, although non-significant (4/4; 100%, p = .125) | Weak (insufficient evidence, meta-analysis required to determine magnitude of effect) |
Coding used to describe strength of the evidence: Highly consistent: vote counting significant at the p < .001 level. Consistent; vote counting significant at the p = .05 level. Insufficient evidence; all in favour, but binomial test non-significant, Inconsistent: highly mixed. Magnitude of effect; small (OR of between .30 and .20), very small (OR below .10). Overall judgement: very strong (highly consistent, largest effect size), strong (highly consistent, small effect size), moderate (consistent, no pooled effect size determined or small to very small effect), weak (insufficient evidence), very weak (inconsistent evidence)