
31Parallel Models
measured in the quadratic form, X + X
2
, because they allow one to present the complete
pattern of the nonlinear relationship. Self-reported health declines from ages 18 to 62 and
then begins to improve. For example, the predicted probability of excellent health decreases
from 0.45 at age 18 to 0.16 at age 62 and then increases to 0.24 by age 88. Additionally, the
predicted probability of fair health increases from 0.10 at age 18 to 0.28 at age 62 and then
decreases to 0.21 by age 88. Age has a much smaller effect on the predicted probability
of poor health, which may be due in part to the relatively small number of responden ...