TABLE 2. Median values of estimates of Fpre, Fpost, and Duration by estimated start year.

Start year	No. of regions	Fpre	Fpost	Duration (years)
Before 1960	88	5.4	1.9	36
1960–64	77	6.1	2.0	31
1965–69	83	6.4	2.2	27
1970–74	85	6.8	2.3	26
1975–79	100	6.8	2.5	23
1980 or later	69	6.7	2.6	19