Plot of partial residuals for log of age at walking versus maternal-hair Hg concentrations for the reduced model with Hg by gender interaction. The partial residual is the natural log of the subject's age at walking adjusted for all variables in the model except Hg. It is computed by adding the Hg effect (estimated coefficient on Hg times the Hg value for that subject) to the raw residual (observed value minus predicted value) obtained from the reduced model. The partial residuals have been rescaled by adding the mean value of log of age at walking to each partial residual. The axis for age at walking (in months) is on a log scale. Outliers are identified on the plot with a different symbol (solid squares). The slope of the solid lines is the regression coefficient for Hg in the originial regression analysis with statistical outliers. The dotted line is the slope with those outliers removed. Source: Myers et al. 1997. Reprinted with permission from NeuroToxicology; copyright 1997, Intox Press.