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Results of subgroup analysis among included studies
| Subgroup | Studies included (N) | Heterogeneity | Pooled WMD | |
|---|---|---|---|---|
| I2 (%) | P value | |||
| Self-control study | 5 | 83 | 0.25 | 0.32 (-0.22–0.86) |
| Asia | 2 | 86 | 0.11 | 0.6 (-0.14–1.35) |
| Publication year: non 2015 | 2 | 0 | 0.05 | 0.4 (-0.01–0.8) |
| Country: Germany | 3 | 11 | 0.08 | -0.26 (-0.56–0.03) |
| Country: Europe | 5 | 70 | 0.58 | -0.11 (-0.49–0.27) |
