Figure 4a illustrates what the difference in intercept between the paternal AAB and low paternal risk groups would be at different ages in the range observed if age had been centered at that point. Age is incremented by 0.25-year intervals, and 95% confidence intervals are provided for each estimate. This approach (D. J. Bauer & Curran, 2005) for probing interactions in mixed models identifies the age at which these two groups would no longer differ significantly in P300 amplitude. The projected age range at which the paternal AAB and low-risk groups would no longer significantly differ was 20.87 years (in Figure 4a, the confidence intervals overlap 0 at this age). These two groups differed significantly at all earlier ages.
