Table 2. Main results of subgroup analyses to explore sources of heterogeneity based on some investigated variables for association between C-reactive protein levels and risk of schizophrenia.

Variables	Heterogeneity (I2 %; Phet)	SMD 95% CI	Pinteraction
Total	18 (92.5; < 0.001)	0.53 (0.30 to 0.76)	NA
Study region			< 0.001
USA	1 (–, –)	0.51 (0.33 to 0.69)
Europe	11 (89.6, < 0.001)	0.42 (0.12 to 0.72)
Asia/Africa	6 (95.3, < 0.001)	0.73 (0.26 to 1.21)
Sample size			0.075
≥ 100	10 (95.5, < 0.001)	0.52 (0.21 to 0.83)
< 100	6 (77.7, < 0.001)	0.63 (0.22 to 1.03)
Clinical setting			< 0.001
Inpatient unit	3 (91.6%, < 0.001)	0.66 (–0.05 to 1.38)
Outpatient unit	3 (92.5%, < 0.001)	0.82 (–0.28 to 1.93)
Both units	8 (84.3, < 0.001)	0.50 (0.24 to 0.76)
Population-based	4 (95.9, < 0.001)	0.31 (0.17 to 0.80)
Mean age			< 0.001
< 30 years	5 (95.9, < 0.001)	0.76 (0.07 to 1.58)
30-50 years	11 (87.7, < 0.001)	0.43 (0.19 to 0.67)
≥ 50 years	2 (84,6, < 0.001)	0.58 (0.03 to 1.12)
Age of onset			< 0.001
≤ 30 years	7 (74.6, 0.001)	0.50 (0.25 to 0.75)
> 30 years	2 (0, 0.591)	0.81 (0.70 to 0.93)
Body mass index			< 0.001
≤ 25 kg/m2	5 (85.1, < 0.001)	0.38 (0.16 to 0.92)
25–30 kg/m2	11 (93.5, < 0.001)	0.60 (0.29 to 0.92)
Adjusted controls			0.077
Yes	13 (93.7, < 0.001)	0.53 (0.23 to 0.84)
No	5 (87.8, < 0.001)	0.54 (0.19 to 0.90)
High-sensitivity CRP assay			0.003
Yes	17 (92.6, < 0.001)	0.56 (0.33 to 0.80)
No	1 (–, –)	0.04 (–0.35 to 0.43)

Abbreviations: CI, confidence interval; CRP, C-reactive protein; het, heterogeneity; NA, not available; SMD, standardized mean difference.