Table 7.

Multivariable regressions of log lead concentration as a function of log copper, log lead in groundwater, and presence of at least one brass part, controlling for relevant covariates.

Variable	Model 1	Model 2	Model 3	Model 4
	Adjusted estimate ($p$-value)	Adjusted estimate ($p$-value)	Adjusted estimate ($p$-value)	Adjusted estimate ($p$-value)
$N$	212	212	104	51
$R^2$	0.08	0.40	0.55	0.66
Country
Ghana	Ref	Ref	Ref	Ref
Mali	0.53 (0.30)	0.41 (0.24)	0.84 (0.29)**	1.15 (0.45)*
Niger	0.78 (0.33)*	0.19 (0.28)	—	—
Water system type
Handpump	Ref	Ref	Ref	Ref
Public tap	0.17 (0.27)	$-0.42$ (0.23)	$-0.17$ (0.38)	$-1.17$ (0.58)*
Age of water system	$-0.012$ (0.012)	$-0.009$ (0.010)	0.001 (0.013)	$-0.026$ (0.028)
Stagnation time	$2.23\times {10}^{-5}$ ($2.9\times {10}^{-4}$)	$6.1\times {10}^{-5}$ ($2.4\times {10}^{-4}$)	$3.5\times {10}^{-4}$ (0.002)	$3.9\times {10}^{-4}$ (0.002)
pH	0.005 (0.004)	0.002 (0.003)	0.024 (0.18)	$-0.14$ (0.26)
Conductivity	$-0.001$ (0.0004)*	$-4.9\times {10}^{-4}$ ($3.1\times {10}^{-4}$)	$1.5\times {10}^{-4}$ ($3.6\times {10}^{-4}$)	$1.3\times {10}^{-4}$ ($3.9\times {10}^{-4}$)
Log copper	—	0.43 (0.04)***	0.39 (0.05)***	0.48 (0.09)***
Log lead in flushed samples (groundwater)	—	—	0.36 (0.14)*	$-0.04$ (0.21)
$\ge 1$ Brass component	—	—	—	1.34 (0.45)**

Note: All models were run using the regress command in STATA. Model 1 (base model) is a simple linear regression of log lead concentration as a function of country, system type, system age, stagnation time, and water sample pH, and conductivity. Model 2 is based on Model 1 but also controls for log copper concentration in water samples. Model 3 is based on Model 2 but also controls for log lead concentration in flushed groundwater samples from sampled sources. Model 4 is based on Model 3 but includes a dummy variable for the presence of one or more brass components identified in the water system. In each model, the $p$-value given is the $p$-value associated with the $F$-value calculated as the mean square model divided by the mean square residual. In each model, the comparator is designated by the abbreviation Ref. —, not applicable; Ref, referent. *$p<0.05$; **$p<0.01$; ***$p<0.001$.