Year	Number
1971	21.09646
1975	25.79755
1976	25.76695
1977	27.08379
1978	26.72385
1979	25.88182
1980	25.0432
1981	24.99682
1982	24.17176
1984	23.44037
1985	23.20191
1986	22.17753
1987	20.91735
1988	19.81811
1989	18.66765
1990	17.9128
1991	17.12731
1992	17.01399
1993	16.9837
1994	16.7637
1995	16.84403
1996	16.92098
1997	17.23117