Table 2. Beta coefficients and 95% CI of child IQ in multiple linear regression analysis in children after adjustment of covariates (n = 445).
| Response variables | Independent variables | Beta coefficients (95% CI) | |||
|---|---|---|---|---|---|
| Model 1 | Model 2 | ||||
| Verbal IQ | A | Per doubling of blood mercury | −2.482(−4.214, −0.749)† | −2.449 (−4.183, −0.716)† | |
| Birth weight, kg | 2.057 (−1.355, 5.469) | 2.112 (−1.302, 5.526) | |||
| Sex of a baby (vs. male) | 3.492 (0.890, 6.094)‡ | 3.372 (0.759, 5.984)‡ | |||
| Maternal age | 0.151 (−0.228, 0.529) | 0.157 (−0.222, 0.535) | |||
| Durbin-Watson | 2.007 | 2.002 | |||
| B | Blood mercury tertile* | T1 | Reference | Reference | |
| T2 | −0.203 (−3.438, 3.032) | −0.179 (−3.414, 3.056) | |||
| T3 | −4.339 (−7.546, −1.132)† | −4.305 (−7.512, −1.098)† | |||
| Birth weight, kg | 1.968 (−1.458, 5.394) | 2.025 (−1.402, 5.452) | |||
| Sex of a baby (vs. male) | 3.361 (0.755, 5.968)‡ | 3.234 (0.618, 5.851)‡ | |||
| Maternal age | 0.155 (−0.224, 0.534) | 0.162 (−0.218, 0.541) | |||
| Durbin-Watson | 2.02 | 2.013 | |||
| Performance IQ | A | Per doubling of blood mercury | −1.683 (−3.707, 0.341) | −1.706 (−3.733, 0.320) | |
| Birth weight, kg | 4.683 (0.696, 8.670)‡ | 4.642 (0.650, 8.634)‡ | |||
| Sex of a baby (vs. male) | 2.940 (−0.100, 5.981) | 3.029 (−0.026, 6.084) | |||
| Maternal age | −0.475 (−0.918, −0.033)‡ | −0.480 (−0.923, −0.037)‡ | |||
| Durbin-Watson | 1.991 | 1.998 | |||
| B | Blood mercury tertile* | T1 | Reference | Reference | |
| T2 | 1.500 (−2.286, 5.286) | 1.484 (−2.305, 5.273) | |||
| T3 | −1.611 (−5.364, 2.142) | −1.633 (−5.389, 2.124) | |||
| Birth weight, kg | 4.453 (0.444, 8.462)‡ | 4.416 (0.402, 8.430)‡ | |||
| Sex of a baby (vs. male) | 2.752 (−0.298, 5.803) | 2.834 (−0.231, 5.899) | |||
| Maternal age | −0.461 (−0.904, −0.017)‡ | −0.465 (−0.909, −0.021)‡ | |||
| Durbin-Watson | 2.008 | 2.011 | |||
| Total IQ | A | Per doubling of blood mercury | −2.402 (−4.279, −0.526)‡ | −2.395 (−4.274, −0.515)‡ | |
| Birth weight, kg | 3.745 (0.049, 7.441)‡ | 3.758 (0.056, 7.460)‡ | |||
| Sex of a baby (vs. male) | 3.474 (0.655, 6.292)‡ | 3.445 (0.612, 6.278)‡ | |||
| Maternal age | −0.162 (−0.573, 0.248) | −0.161 (−0.572, 0.250) | |||
| Durbin-Watson | 1.975 | 1.981 | |||
| B | Blood mercury tertile* | T1 | Reference | Reference | |
| T2 | 0.965 (−2.542, 4.471) | 0.972 (−2.539, 4.482) | |||
| T3 | −3.449 (−6.925, 0.027) | −3.439 (−6.920, 0.041) | |||
| Birth weight, kg | 3.539 (−0.174, 7.252) | 3.556 (−0.163, 7.275) | |||
| Sex of a baby (vs. male) | 3.276 (0.451, 6.101)‡ | 3.240 (0.400, 6.079)‡ | |||
| Maternal age | −0.150 (−0.561, 0.261) | −0.148 (−0.560, 0.263) | |||
| Durbin-Watson | 1.997 | 1.998 | |||
The covariates in Model 1 were: child birth weight and sex, maternal age, maternal educational level, household income, and fish intake. The covariates in Model 2: included all those from Model 1 plus maternal blood lead.
CI = confidence interval.
*Blood mercury level: 1st tertile (≤ 2.622), 2nd tertile (2.622–3.829), 3rd tertile (> 3.829); † P < 0.010; ‡ P < 0.050.