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There are 11 studies included in the water improvement intervention group, with dates of publication ranging from 1987 to 2014. The total study population observed was 119,936 (Table 1). Based on χ2 = 114.36 (P < 0.01), there emerged a low degree of inter-study heterogeneity, and a random-effects model should be used for combined RR. The overall pooled estimate indicates that water improvement interventions are effective in reducing diarrheal disease (random-effects model RR 0.48, 95% CI 0.42–0.54). In the sub-group with water sample tested (n = 3), the RR was 0.44 (0.28–0.67), while the RR was 0.55 (0.49–0.61) in the no water sample tested group (n = 8).

Table 1

Summary of included water improvement intervention studies

 Intervention group
Control group
Authors and publishing yearNo. of casesStudy populationNo. of casesStudy populationWeight (%)RR95% CI
Zhang & Huo (1987)  4,057 29,328 5,596 19,312 12.3 0.48 0.46 ∼ 0.49 
Wang et al. (1989)  321 1,816 767 2,685 11.3 0.62 0.55 ∼ 0.69 
Lou et al. (1989)  608 2,154 392 842 11.6 0.61 0.55 ∼ 0.67 
Chen et al. (1999)  95 1,341 179 1,676 8.8 0.66 0.52 ∼ 0.84 
Zhu & Xia (1997)  129 1,733 320 1,739 9.7 0.40 0.33 ∼ 0.49 
Zhang et al. (2000)  331 1,172 867 1,864 11.5 0.61 0.55 ∼ 0.67 
Gu et al. (2000)  176 6,211 315 5,951 10.0 0.54 0.45 ∼ 0.64 
Chen (2006)  781 15,159 1,444 14,746 11.8 0.53 0.48 ∼ 0.57 
Wang (2011)  42 2,721 197 2,780 6.9 0.21 0.15 ∼ 0.30 
Tang et al. (2011)  2,839 26 1,024 1.1 0.04 0.01 ∼ 0.14 
Wang et al. (2014)  23 1389 104 1404 5.0 0.22 0.14 ∼ 0.35 
 Intervention group
Control group
Authors and publishing yearNo. of casesStudy populationNo. of casesStudy populationWeight (%)RR95% CI
Zhang & Huo (1987)  4,057 29,328 5,596 19,312 12.3 0.48 0.46 ∼ 0.49 
Wang et al. (1989)  321 1,816 767 2,685 11.3 0.62 0.55 ∼ 0.69 
Lou et al. (1989)  608 2,154 392 842 11.6 0.61 0.55 ∼ 0.67 
Chen et al. (1999)  95 1,341 179 1,676 8.8 0.66 0.52 ∼ 0.84 
Zhu & Xia (1997)  129 1,733 320 1,739 9.7 0.40 0.33 ∼ 0.49 
Zhang et al. (2000)  331 1,172 867 1,864 11.5 0.61 0.55 ∼ 0.67 
Gu et al. (2000)  176 6,211 315 5,951 10.0 0.54 0.45 ∼ 0.64 
Chen (2006)  781 15,159 1,444 14,746 11.8 0.53 0.48 ∼ 0.57 
Wang (2011)  42 2,721 197 2,780 6.9 0.21 0.15 ∼ 0.30 
Tang et al. (2011)  2,839 26 1,024 1.1 0.04 0.01 ∼ 0.14 
Wang et al. (2014)  23 1389 104 1404 5.0 0.22 0.14 ∼ 0.35 

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