Internal exposure levels of polycyclic aromatic hydrocarbons in children and adolescents: a systematic review and meta-analysis

Table 4 Subgroup analysis on differences of level of 1-OHPyr in children and adolescents with different living condition

Character	Subgroup	No. studies	SMD	95% CI		Heterogeneity			Begg’s test		Egger’s test
Character	Subgroup	No. studies	SMD	Lower	Upper	χ²	P	I² (%)	z	P	t	P
Overall		16	0.21	0.03	0.40	82.57	< 0.01	82	0.77	0.44	1.32	0.21
Countries (Additional file 1: Figure S1)	Developed	7	0.06	− 0.12	0.23	18.05	< 0.01	67	− 0.45	0.65	0.05	0.98
Countries (Additional file 1: Figure S1)	Developing	9	0.37	0.03	0.72	53.81	< 0.01	85	0.21	0.84	3.28	0.41
Age (Additional file 1: Figure S2)	≤ 6 years	3	0.26	− 0.33	0.86	14.51	< 0.01	86	0.00	1.00	1.15	0.46
Age (Additional file 1: Figure S2)	7–18 years	11	0.19	− 0.05	0.43	56.93	< 0.01	82	0.47	0.64	0.98	0.35
Gender (Additional file 1: Figure S3)	Boys only	3	0.03	− 0.40	0.45	4.42	0.11	55	1.57	0.12	5.58	0.02
Gender (Additional file 1: Figure S3)	Both genders	13	0.25	0.04	0.46	76.37	< 0.01	84	1.10	0.27	2.35	0.17
Data (Additional file 1: Figure S4)	Original	12	0.21	0.00	0.42	55.76	< 0.01	80	0.69	0.49	1.70	0.22
Data (Additional file 1: Figure S4)	Estimating	4	0.22	− 0.24	0.69	25.27	< 0.01	88	− 0.68	0.49	0.58	0.96
Study period (Additional file 1: Figure S5)	1994–2000	5	0.25	− 0.16	0.66	25.49	< 0.01	84	0.24	0.81	1.63	0.77
	2001–2010	8	0.27	0.04	0.50	31.19	< 0.01	78	0.87	0.39	2.17	0.16
	2011–2015	3	0.02	− 0.66	0.69	21.24	< 0.01	91	1.04	0.30	19.77	0.40
Sample collection season (Additional file 1: Figure S6)	Spring	5	0.37	− 0.04	0.77	38.48	< 0.01	90	1.47	0.14	3.61	0.25
	Winter	5	0.12	− 0.11	0.35	5.83	0.21	31	0.00	1.00	0.18	0.93
	Unclear	6	0.17	− 0.19	0.53	37.93	< 0.01	87	0.94	0.35	3.28	0.53

ISSN: 1347-4715