Year	Number
1961	1.1403508771929824
1962	1.293103448275862
1963	1.6694915254237288
1964	2.9749999999999996
1965	3.278688524590164
1966	3.6290322580645165
1967	3.968253968253968
1968	4.263565891472868
1969	4.393939393939394
1970	4.5588235294117645
1971	4.642857142857143
1972	4.758620689655172
1973	4.9
1974	5.769230769230769
1975	6.172839506172839
1976	6.547619047619048
1977	7.471264367816093
1978	8.379888268156424
1979	9.239130434782608
1980	10.052910052910052
1981	10.824742268041238
1982	12.060301507537687
1983	12.272727272727273
1984	12.76595744680851
1985	13.333333333333334
1986	14.444444444444443
1987	15.172413793103448
1988	16.39344262295082
1989	17.5
1990	19.174041297935105
1991	19.837943559653535
1992	21.91780821917808
1993	23.420479302832245
1994	25.36133078811017
1995	25.906976744186043
1996	26.055951727921013
1997	26.380873866446823
1998	26.92328842452571