Table 2 Subgroup analysis
Subgroup variable |  | No of studies | Prevalence (%) (95% CI) | P-value of Cochran’s Q test for heterogeneity | I2 (%) | P-value of test for subgroup differences |
|---|---|---|---|---|---|---|
Publication year | ≥ 2020 | 12 | 19.2 (13.8, 25.3) | 0.000 | 92.4 | 0.839 |
|  | < 2020 | 17 | 20.0 (15.1, 25.4) | 0.000 | 91.4 | |
Risk of bias | Low | 5 | 21.3 (11.9, 32.5) | 0.000 | 95.1 | 0.931 |
| Â | Moderate | 14 | 19.7 (15.5, 24.3) | 0.000 | 88.9 | |
| Â | High | 10 | 18.5 (10.7, 27.8) | 0.000 | 92.8 | |
Study design | Cross-sectional | 20 | 19.0 (14.9, 23.5) | 0.000 | 90.9 | 0.660 |
| Â | Case-control | 9 | 21.1 (13.8, 29.4) | 0.000 | 93.3 | |
Sample size | ≥ 150 | 15 | 18.5 (13.8, 23.7) | 0.000 | 94.5 | 0.439 |
|  | < 150 | 14 | 21.2 (16.0, 26.9) | 0.000 | 81.3 | |
Mean age | ≥ 25 | 14 | 19.4 (14.2, 25.2) | 0.000 | 92.5 | 0.810 |
|  | < 25 | 14 | 20.4 (15.0, 26.4) | 0.000 | 91.6 | |
Mean BMI | ≥ 25 | 16 | 22.5 (17.0, 28.5) | 0.000 | 92.9 | 0.418 |
|  | < 25 | 7 | 18.4 (11.3, 26.7) | 0.000 | 89.1 | |
Upper reference limit of TSH | 2.5 ≤ upper limit < 4 | 9 | 28.6 (21.6, 36.3) | 0.000 | 90.7 | 0.003 |
|  | 4 ≤ upper limit ≤ 5.5 | 14 | 16.1 (11.9, 20.8) | 0.000 | 90.8 | |
All studies | Â | 29 | 19.7 (16.1, 23.5) | 0.000 | 91.5 | - |