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Table 6 Univariate random effects meta-regression (methods of moments) and subgroup analyses for EDUCATIONAL ATTAINMENT

From: Determinants of participation in voluntary work: a systematic review and meta-analysis of longitudinal cohort studies

  Subgroup analyses Results from meta-regression
Results Heterogeneity
Variable Subgroup Number of studies OR 95% CI P-value I 2 Coefficient SD P-value
Outcome measurement Mixed 3 1.199 0.985–1.460 0.000 90% Reference
Formal 10 (14 different samples) 1.153 1.094–1.215 0.000 81% −0.0335 0.0591 0.571
Determinant measurement Dichotomous 5 (9 different samples) 1.256 1.001–1.577 0.000 86% Reference
Continuous 8 1.130 1.082–1.179 0.000 80% −0.0922 0.0579 0.111
Proportion of volunteers (%) in baseline study sample Continuous 9a (13 different samples) 1.162 1.104–1.223 0.000 79% −0.0001 0.0001 0.176
0–100% 10 1.147 1.088–1.208 0.000 87% Reference   
0% 2 (3 different samples) 1.564 1.321–1.853 0.667 0% 0.3080 0.1100 0.005
100% 3 (4 different samples) 1.171 0.870–1.577 0.024 68% 0.0083 0.0720 0.908
Mean age at baseline Continuous 10b (13 different samples) 1.111 1.064–1.161 0.000 77% 0.0001 0.0001 0.493
≤ 55 years 7 (8 different samples) 1.148 1.025–1.286 0.000 84% Reference   
>  55 years 7 (9 different samples) 1.203 1.128–1.284 0.000 84% 0.0711 0.0576 0.217
Continent USA 6 1.144 1.075–1.218 0.000 84% Reference
Europe 6 (10 different samples) 1.186 1.055–1.333 0.000 77% 0.0110 0.0598 0.854
Australia 1 1.430 1.283–1.594 N.A. N.A. 0.2164 0.1049 0.039
Year of baseline measurement Continuous 13 (17 different samples) 1.171 1.114–1.232 0.000 83% N.A.   
<  2006 11 (13 different samples) 1.187 1.125–1.252 0.000 86% Reference   
≥ 2006 3 (4 different samples) 1.081 0.852–1.372 0.132 47% −0.1167 0.0810 0.150
Duration of follow-up Continuous 13 (17 different samples) 1.171 1.114–1.232 0.000 83% N.A.   
≤ 3 years 5 (9 different samples) 1.241 1.114–1.382 0.003 66% Reference   
4–7 years 2 1.062 0.974–1.157 0.104 62% −0.1728 0.1068 0.106
≥ 8 years 6 1.225 1.081–1.389 0.000 91% −0.0225 0.0840 0.789
Risk of bias items
 Study participation Unclear/high risk of bias 3 (4 different samples) 1.144 1.089–1.203 0.000 84% Reference
Low risk of bias 11 (13 different samples) 1.396 0.973–2.004 0.007 75% 0.1620 0.0766 0.034
 Study confounding Unclear/high risk of bias 2 1.199 1.089–1.321 0.387 0% Reference
Low risk of bias 11 (15 different samples) 1.171 1.110–1.235 0.000 85% −0.0105 0.0880 0.905
  1. aThe studies of Ajrouch et al. (2014), Bartels et al. (2013), Parkinson (2010) and Voorpostel & Coffé (2014) are not included in this analysis, because the proportion of volunteers (%) in the baseline study sample is not reported
  2. bThe studies of Bartels et al. (2013), Hank & Erlinghagen (2010) and Parkinson (2010) are not included in this analysis, because the mean age at baseline is not reported
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