 woman is 20 years old, the probability is about .20 whereas when a woman is 80, the probability is about 0.80. In essence, the marginal effect of <code>age</code> reported above is the slope of this predicted probability plot at the mean age of women in the dataset (which is 31.3162651). Clearly, this quantity is useful (it’s the impact of age for the average-aged woman) but the logit curve shows that the marginal effect of <code>age</code> differs considerably across ages and, as we know from above with