Table 3.
Unadjusted and Adjusted Changes in IQ for Each Increase in the Blood Lead Concentration of 1 µg per Deciliter for All Children in the Study.*
| Type of Blood Lead Measurement |
No. of Children |
At 3 Years of Age | At 5 Years of Age | Overall | |||
|---|---|---|---|---|---|---|---|
| β±SE (95% CI) | P Value | β±SE (95% CI) | P Value | β±SE (95% CI) | P Value | ||
| Unadjusted estimate† | |||||||
| Lifetime average | 172 | −0.74±0.18 (−1.09 to −0.39) |
<0.001 | −1.00±0.19 (−1.38 to −0.63) |
<0.001 | −0.87±0.16 (−1.19 to −0.55) |
<0.001 |
| Peak | 172 | −0.40±0.11 (−0.62 to −0.18) |
<0.001 | −0.47±0.11 (−0.70 to −0.25) |
<0.001 | −0.44±0.10 (−0.63 to −0.24) |
<0.001 |
| Concurrent‡ | 171 | −0.60±0.15 (−0.89 to −0.31) |
<0.001 | −1.02±0.19 (−1.38 to −0.65) |
<0.001 | −0.81±0.14 (−1.09 to −0.53) |
<0.001 |
| Average in infancy (6–24 mo) |
172 | −0.73±0.21 (−1.15 to −0.31) |
<0.001 | −0.97±0.22 (−1.40 to −0.54) |
<0.001 | −0.85±0.19 (−1.23 to −0.47) |
<0.001 |
| Adjusted estimate§ | |||||||
| Lifetime average | 172 | −0.35±0.17 (−0.69 to 0.00) |
0.05 | −0.57±0.18 (−0.93 to −0.20) |
0.003 | −0.46±0.15 (−0.76 to −0.15) |
0.004 |
| Peak | 172 | −0.19±0.10 (−0.39 to 0.01) |
0.06 | −0.26±0.11 (−0.47 to −0.05) |
0.02 | −0.23±0.09 (−0.40 to −0.05) |
0.01 |
| Concurrent‡ | 171 | −0.31±0.15 (−0.60 to −0.01) |
0.04 | −0.61±0.19 (−0.99 to −0.24) |
<0.001 | −0.46±0.14 (−0.74 to −0.18) |
0.002 |
| Average in infancy (6–24 mo) |
172 | −0.32±0.20 (−0.71 to 0.07) |
0.10 | −0.53±0.20 (−0.93 to −0.13) |
0.01 | −0.43±0.17 (−0.77 to −0.09) |
0.02 |
The lifetime average blood lead concentration was estimated at the ages of 3 and 5 years by computing the area under the blood lead curve (AUC) from 6 through 36 months and from 6 through 60 months, respectively, and then dividing the AUC by its corresponding age span to yield an average on the microgram-per-deciliter scale. The peak blood lead concentration was the child’s highest measured blood lead concentration through the age of three or five years. The concurrent blood lead concentration was the concentration measured on the day of cognitive testing, and the average blood lead concentration in infancy was the AUC from 6 through 24 months. CI denotes confidence interval. /3 values are the estimated unstandardized regression coefficients.
The unadjusted model includes only classification factors for age and for individual children.
One child was lacking a concurrent blood lead measurement at the age of three years.
Estimates were adjusted for maternal IQ, race, level of education, use of tobacco during pregnancy, household income, and Home Observation for Measurement of Environment Inventory score, and the child’s sex, birth weight, and iron status.