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Table 3 Univariate random effects meta-regression (methods of moments) and subgroup analyses for AGE

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 2 0.986 0.959–1.013 0.037 77% Reference
Formal 9 (12 different samples) 0.969 0.946–0.992 0.000 89% −0.0168 0.0251 0.504
Determinant measurement Dichotomous 1 (2 different samples) 0.485 0.385–0.611 0.248 25% Reference
Continuous 10 (12 different samples) 0.983 0.969–0.996 0.000 78% 0.7122 0.1014 0.000
Proportion of volunteers (%) in baseline study sample Continuous 10a (13 different samples) 0.970 0.950–0.991 0.000 88% 0.0000 0.0001 0.591
0–100% 9 (11 different samples) 0.985 0.971–0.999 0.000 79% Reference   
0% 1 0.440 0.343–0.565 N.A. N.A. −0.8053 0.1292 0.000
100% 2 0.747 0.444–1.256 0.001 91% −0.0500 0.0292 0.087
Mean age at baseline Continuous 10b (12 different samples) 0.983 0.969–0.996 0.000 78% −0.0000 0.0000 0.200
≤ 55 years 5 (6 different samples) 0.991 0.975–1.007 0.000 79% Reference   
>  55 years 6 (8 different samples) 0.944 0.904–0.986 0.000 89% −0.0296 0.0198 0.135
Continent USA 6 0.978 0.959–0.998 0.001 77% Reference
Europe 5 (8 different samples) 0.966 0.933–1.000 0.000 91% −0.0026 0.0210 0.900
Year of baseline measurement Continuous 11 (14 different samples) 0.989 0.984–0.995 0.000 87% 0.0006 0.0014 0.686
<  2006 8 (10 different samples) 0.970 0.948–0.993 0.000 91% Reference   
≥ 2006 3 (4 different samples) 0.975 0.959–0.991 0.388 1% 0.0110 0.0230 0.631
Risk of bias items
 Study participation Unclear/high risk of bias 9 (12 different samples) 0.975 0.956–0.995 0.000 88% Reference
Low risk of bias 2 0.858 0.623–1.192 0.000 93% −0.0099 0.0315 0.754
 Study confounding Unclear/high risk of bias 1 1.000 0.981–1.020 N.A. N.A. Reference
Low risk of bias 10 (13 different samples) 0.970 0.950–0.991 0.000 88% −0.0303 0.0331 0.360
  1. aThe study of Ajrouch et al. (2014) is not included in this analysis, because the proportion of volunteers (%) in the baseline study sample is not reported
  2. bThe study of Hank & Erlinghagen (2010) is not included in this analysis, because the mean age at baseline is not reported
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