Year	Number
1961	0.46875
1962	0.515625
1963	0.546875
1964	0.578125
1965	0.8593750000000001
1966	1.0153846153846153
1967	1.5384615384615385
1968	3.0395136778115504
1969	6
1970	4.451127819548873
1971	4.865671641791044
1972	5
1973	5
1974	4.864864864864865
1975	5.066666666666666
1976	5.263157894736842
1977	5.454545454545454
1978	5.67741935483871
1979	5.769230769230769
1980	5.948717948717949
1981	8.512820512820513