Year	Number
1970	24.11
1971	24.77941
1972	22.86364
1973	20.28626
1974	19.47727
1975	17.56475
1976	19.74409
1977	21.01481
1978	22.89781
1979	20.66129
1984	22.62117
1985	22.89181
1986	22.50069
1987	22.53402
1988	23.03684
1989	23.01289