Table 2:

Estimated Covariance and Covariate Effects in the GENEVA Data.

Parameters	Estimate
Covariance Components
${\sigma }^{2*}$	33.211
${\sigma }_a^2/{\sigma }^2$	0.4437
${\sigma }_e^2/{\sigma }^2$	0.5563
Covariate Effects	Estimate (SE)	p-value
Sex: Female	0.930 (0.468)	0.0471
Age	0.225 (0.020)	< 2 × 10−16
Water source: Well	0.185 (0.620)	0.766
Water source: Other	1.669 (1.682)	0.321
Brush frequency†	0.674 (0.348)	0.053
Saliva flow	−0.180 (0.582)	0.758
Home water fluoride level	0.714 (0.610)	0.243
Education level§	−0.612 (0.374)	0.103
S. mutans	2.134 (0.523)	5.13 × 10−5
Intercept	−1.365 (1.546)	0.378

Note: $*{\sigma }^2={\sigma }_a^2+{\sigma }_e^2$

^†: Brush frequency coded as: 1= more than 3 times per day, 2 = 3 times per day, 3 = 2 times per day, 4 = once a day, 5 = less than once a day. In the final samples, category 1 has zero observations, so category 2 is treated as the reference group.

^§: Education level is coded as: 1 = up to high school, 2 = some college, 3 = four-year degree or beyond.