Table 3.

Causal effect of tooth loss on possible major depression (PHQ-8 ⩾ 10); N = 169 061

	Coef.	95% CI	p-Value	F-statistic
Treatment variable: number of lost teeth
OLS estimation
The number of lost teeth (continuous)	0.0073	0.0071–0.0075	<0.001	–
2SLS estimation
Second stage
The number of lost teeth (continuous)	0.0081	−0.0012 to 0.0173	0.087	–
First stage
Drinking water fluoridea	−0.5640	−0.6931 to −0.4350	<0.001	73.4
Reduced form
Drinking water fluoridea	−0.0046	−0.0099 to 0.0008	0.092	–
Treatment variable: having lost ⩾1 tooth
OLS estimation
Having lost ⩾1 tooth (ref. full dentition)	0.0840	0.0811–0.0870	<0.001	–
2SLS estimation
Second stage
Having lost ⩾1 tooth (ref. full dentition)	0.1739	−0.0289 to 0.3766	0.093	–
First stage
Drinking water fluoridea	−0.0262	−0.0348 to −0.0177	<0.001	36.1
Reduced form
Drinking water fluoridea	−0.0046	−0.0099 to 0.0008	0.092	–
Treatment variable: having lost all tooth
OLS estimation
Having lost all teeth (ref. having ⩾1 tooth)	0.1308	0.1245 to 0.1372	<0.001	–
2SLS estimation
Second stage
Having lost all teeth (ref. having ⩾1 tooth)	0.4013	−0.0732 to 0.8759	0.097	–
First stage
Drinking water fluoridea	−0.0114	−0.0153 to −0.0074	<0.001	31.7
Reduced form
Drinking water fluoridea	−0.0046	−0.0099 to 0.0008	0.092	–

CI, confidence interval; OLS, Ordinary Least Squares; PHQ-8, the eight-item Patient Health Questionnaire depression scale; 2SLS, two-stage least-squares.

Adjusted for year of birth, wave of survey, gender and state of residence.

^aSum of the proportion of people supplied with fluoridated water in the county of residence during the age of 5–14 years (rescaled between 0 and 1).