|
Category
|
Subgroup
|
Number of studies
|
Proportion estimate (%) and 95% CI
|
Heterogeneity
|
|---|
|
I2
|
P-value
|
|---|
|
Study period
|
2011–2013
|
6
|
27.7 (21.8, 33.7)
|
95.8%
|
< 0.01
|
|
2014–2016
|
7
|
18.9 (14.3, 23.5)
|
97.1%
|
< 0.01
|
|
Study site
|
Northern China
|
6
|
26.0 (21.1, 31.0)
|
95.9%
|
< 0.01
|
|
Southern China
|
5
|
22.4 (14.6, 30.2)
|
97.7%
|
< 0.01
|
|
Othera
|
4
|
22.5 (15.8, 29.2)
|
97.6%
|
< 0.01
|
|
Sample size
|
≤1000
|
7
|
28.4 (20.4, 36.3)
|
97.1%
|
< 0.01
|
|
> 1000
|
8
|
20.3 (15.8, 24.8)
|
98.0%
|
< 0.01
|
|
Data collection method
|
Self-administrated questionnaire
|
6
|
25.2 (17.2, 33.3)
|
98.2%
|
< 0.01
|
|
Face-to-face interview
|
9
|
23.1 (19.3, 26.9)
|
96.5%
|
< 0.01
|
|
Recall window of nitrite inhalants use (months)
|
3
|
6
|
23.7 (18.3, 29.2)
|
96.1%
|
< 0.01
|
|
6
|
7
|
22.0 (16.4, 27.5)
|
98.1%
|
< 0.01
|
|
12
|
2
|
31.4 (11.3, 51.5)
|
98.3%
|
< 0.01
|
|
Publication language
|
English
|
7
|
27.6 (20.0, 35.2)
|
98.5%
|
< 0.01
|
|
Chinese
|
8
|
20.8 (16.9, 24.8)
|
96.0%
|
< 0.01
|
- a These studies were not conducted in one district; Zhao et al. (2017) was a nation-wide online survey, Wang et al. (2017) was conducted in Beijing and Nanjing, Dong (2017) was conducted in Shanghai and Tianjin, and Li (2014) was conducted in seven cities in China
