Year	Number
1961	3.0578512396694215
1962	3.524590163934426
1963	3.495934959349593
1964	3.467741935483871
1965	3.44
1966	3.492063492063492
1967	3.4375000000000004
1968	3.4375000000000004
1969	3.3846153846153846
1970	3.4615384615384617
1971	3.3834586466165413
1972	3.260869565217391
1973	3.146853146853147
1974	2.705882352941176
1975	2.804878048780488
1976	2.8220858895705523
1977	2.764705882352941
1978	2.598870056497175
1979	2.7710843373493974
1980	2.8301886792452833
1981	2.430939226519337
1982	2.178217821782178
1983	2.349726775956284