region. Two broad approaches are available for BMD calculations that are based on continuous outcomes. As described above, one option is to fix P₀ at a specified percentile of performance in the unexposed population (e.g., 0.05 or 0.10). Assuming that the data follow a linear model (Y_i = a₀ + a₁X _i + ε_i, where X _i represents the exposure level for the ith subject, a₀ and a₁ are unknown regression coefficients, and ε_i is random error, assumed to be normally distributed with variance σ₂), specifying a fixed P₀ is equivalent to setting the cutoff value at a specified number of SDs below the mean in the unexposed group:

C = a₀ + σΦ^-1 (P₀),

where Φ (×) represents the normal cumulative distribution function (i.e., the area under a standard normal curve up to and including the value ×). When P₀ = 0.05, for example, the value of C is a₀ −1.645 σ (i.e., 1.64 SDs below the control mean). Alternatively, one can choose the cutoff

Front Matter (R1-R20)

Executive Summary (1-12)

Introduction (13-30)

Chemistry, Exposure, Toxicokinetics, and Toxicodynamics (31-71)

Biological Variability (72-104)

Dose Estimation (105-146)

Health Effects of Methylmercury (147-249)

Comparison of Studies for Use in Risk Assessment (250-270)

Dose-Response Assessment (271-303)

Risk Characterization and Public Health Implications (304-332)

Appendix to Chapter 7 (333-336)

Glossary (337-344)