Good studies from the different research eras can be used to illustrate how lead effect sizes have changed over time.
Landrigan et al. (1975) represents the Early Era. In this study, there were 46 children in the high lead group and 78 in the control group. Their respective BLLs were 48.3 and 26.9 in 1972 and 40.5 and 26.5 in 1973, and they were 8.3 and 9.3 years old, respectively. So we have a gigantic 14 μg/dL gap between these groups. The high lead group had an average IQ of 88.02 versus 92.88 for the low lead group, or a 4.86 point IQ gap, and thus a per μg effect of 0.35 IQ points.
Baghurst et al. (1992) represents the Middle Era. In this study, there were 494 children who had IQ results, and they were divided into quartiles by BLLs. The mean concentrations of blood at assessment age were 6.6 μg/dL for the lowest quartile, 10.1 for the second, 13.7 for the third, and 20.0 for the final one. Their IQs were 109.6, 107.7, 102.7, and 98.7, respectively. Going from the lowest to the highest lead exposure quartiles, we have a BLL difference of 13.4 μg/dL and an IQ difference of 10.9 points. Going quartile to quartile, the effect of 1 μg of lead was 0.54 IQ points, 1.39 IQ points, and then 0.63 IQ points, with the aggregate (1 - 4) being 0.81 IQ points.
Kim, Yu & Lee (2010) represents the the Modern Era. In this study, there were 302 children who were median-split by BLLs. The high BLL group had a mean BLL of 3.74 and the low BLL group had a mean of 1.92 with IQs of 106.4 and 110, respectively. These differences of 1.82 μg/dL and 3.60 IQ points mean that the per μg/dL IQ drop was 1.98 points.
What is the effect of 1 μg of lead on IQ?
Good studies from the different research eras can be used to illustrate how lead effect sizes have changed over time.
Landrigan et al. (1975) represents the Early Era. In this study, there were 46 children in the high lead group and 78 in the control group. Their respective BLLs were 48.3 and 26.9 in 1972 and 40.5 and 26.5 in 1973, and they were 8.3 and 9.3 years old, respectively. So we have a gigantic 14 μg/dL gap between these groups. The high lead group had an average IQ of 88.02 versus 92.88 for the low lead group, or a 4.86 point IQ gap, and thus a per μg effect of 0.35 IQ points.
Baghurst et al. (1992) represents the Middle Era. In this study, there were 494 children who had IQ results, and they were divided into quartiles by BLLs. The mean concentrations of blood at assessment age were 6.6 μg/dL for the lowest quartile, 10.1 for the second, 13.7 for the third, and 20.0 for the final one. Their IQs were 109.6, 107.7, 102.7, and 98.7, respectively. Going from the lowest to the highest lead exposure quartiles, we have a BLL difference of 13.4 μg/dL and an IQ difference of 10.9 points. Going quartile to quartile, the effect of 1 μg of lead was 0.54 IQ points, 1.39 IQ points, and then 0.63 IQ points, with the aggregate (1 - 4) being 0.81 IQ points.
Kim, Yu & Lee (2010) represents the the Modern Era. In this study, there were 302 children who were median-split by BLLs. The high BLL group had a mean BLL of 3.74 and the low BLL group had a mean of 1.92 with IQs of 106.4 and 110, respectively. These differences of 1.82 μg/dL and 3.60 IQ points mean that the per μg/dL IQ drop was 1.98 points.