Year	Number
1972	19.20833
1973	19.872
1974	19.136
1975	18.984
1976	20
1977	20.816
1978	20.76744
1979	20.76744
1980	20.76744
1982	22.42424
1983	21.42143
1984	21.04138
1985	22.0604
1986	16.46305
1987	14.45175
1988	13.8961
1989	15.29817
1990	15.48198
1991	15.5
1992	13.69549