Year	Number
1961	5.88235294117647
1962	8.823529411764707
1963	10.588235294117647
1964	13.141176470588237
1965	12.494117647058824
1966	12.447058823529412
1967	12.4
1968	12.352941176470589
1969	12.305882352941175
1970	12.258823529411766
1971	12.211764705882352
1972	12.16470588235294
1973	12.117647058823529
1974	12.070588235294117
1975	11.355555555555556
1976	11.31111111111111
1977	11.266666666666666
1978	10.631578947368421
1979	10.589473684210526
1980	10.547368421052632
1981	10.505263157894737
1982	9.466666666666667
1983	9.428571428571429
1984	8.57391304347826
1985	8.183333333333334
1986	8.15
1987	7.792000000000001
1988	7.461538461538461
1989	7.430769230769231
1990	7.125925925925926
1991	6.8428571428571425
1992	6.814285714285714
1993	6.785714285714286
1994	6.757142857142857
1995	6.279999999999999
1996	5.8625
1997	5.188888888888889
1998	4.894736842105263
1999	5.07012987012987
2000	4.921518987341772
2001	4.76847290640394
2002	4.611337000717532
2003	4.587813620071684
2004	4.78
2005	4.5175