Figure 1.

(a) The number of prescriptions in the six months up to conception is roughly stable up to age 30, then increases supra-linearly with age up to about age 55, after which it increases linearly with age at about 1 prescription per 10 years of age. (b) A simulation where both the mean and variability (standard deviation) of the age distribution increase linearly over calendar time. The pastel red dots demonstrate what would happen if the variability trend stopped at the 21^st year. Assumed is a normal distribution with parameters taken approximately from reference 20, with sufficient detail to prove the principle. For the turquoise dots, the mean is assumed to increase from 30 to 33 years by 0.1 year per year, while the standard deviation increases from 5 to 8 years, also by 0.1 year per year. For the pastel red dots, the mean trend is identical, but the standard deviation is kept constant at 7 from year 21 onwards.