Do you think that it might have had something to do with the change in the denominator?
The number of starters per year went from 29,000 in 1960 to over 80,000 in 1985.
Between 1960 and 1975 the number of starters went from 29,000 to 58,000 I.e. doubled.
Once again Thomarse you've proven statistics are not your forte.