formed for both maternal-hair and cord-blood Hg. Methods similar to those reported by Crump et al. (1998) were used, fixed P₀ values being 0.05 and 0.16 and excess risks (BMRs) being 5% and 10%. For comparability, the committee requested that the Crump analyses on the Seychelles and New Zealand data be expanded to include BMD and BMDL calculations for P₀ = 0.05 and 0.16 and for BMR = 0.05 and 0.10. The committee requested these analyses only for the outcomes measured when the children were 5 to 7 years old, because that age period was the only one available from the Faroe Islands study, and data from that age group have better predictive ability than data from earlier ages (E. Budtz-Jørgensen, Copenhagen University, N. Keiding, Copenhagen University, and P. Grandjean, University of Southern Denmark, unpublished material, May 5, 2000). For the Seychelles study, six 66-month end points were considered: Bender Gestalt errors, Child Behavior Checklist-Total, McCarthy-General Cognitive Index, Preschool Language-Total Score, Woodcock-Johnson Applied Problems, and Woodcock-Johnson Letter-Word recognition. For reasons to be discussed in more detail presently, the focus here is on calculations derived from the K-power model applied with P₀ = 0.05 and BMD = 0.05. The results of these analyses are summarized in Table 7-2 and graphically represented in Figure 7-3.

Table 7-2 and Figure 7-3 reveal some interesting patterns. First, we see that although study-to-study variability is substantial, within-study consistency (i.e., outcome to outcome) is relatively high. BMDs tended to be lowest for the New Zealand study. BMD and BMDL estimates for the Seychelles study tended to be either nonexistent or quite large (nonexistent values or values greater than 100 are indicated by asterisks in the table). Despite the substantial variability, however, the analyses yield a range of BMD values that are moderately consistent across the three studies. The next section discusses how those data might be used as the basis for a risk assessment.

An important step in the risk-assessment process is choosing an appropriate dose to be used as the “point of departure” (i.e., choosing the dose to which uncertainty factors will be applied to estimate an