Schroeder S R, Hawk B, Otto D A, Mushak P, Hicks R E
Environ Res. 1985 Oct;38(1):144-54. doi: 10.1016/0013-9351(85)90080-5.
Initial evaluations of 104 low-socioeconomic status black children screened by the local community health departments in North Carolina showed significant effects of lead in the range 6-59 micrograms/dl on IQ after controlling for concomitant social factors, such as socioeconomic status, home environment, and maternal IQ. The main concomitant variable was socioeconomic status, which was multicolinear with other social factors. Five years later, when all blood lead levels were 30 micrograms/dl or less, lead effects on IQ were no longer significant. The correlation between maternal and child IQ, which had been suppressed initially in children with higher lead levels, returned to expected levels when decreases in blood lead level occurred, while concomitant variables remained stable over the 5-year period.
对北卡罗来纳州当地社区卫生部门筛查的104名社会经济地位较低的黑人儿童进行的初步评估显示，在控制了诸如社会经济地位、家庭环境和母亲智商等伴随社会因素后，血铅水平在6 - 59微克/分升范围内对智商有显著影响。主要的伴随变量是社会经济地位，它与其他社会因素存在多重共线性。五年后，当所有血铅水平都在30微克/分升或更低时，铅对智商的影响不再显著。母亲和孩子智商之间的相关性，最初在血铅水平较高的孩子中受到抑制，当血铅水平下降时恢复到预期水平，而伴随变量在这5年期间保持稳定。
