Year	Number
1961	5.633500161258213
1962	6.010261253405551
1963	6.606268160763352
1964	7.142399906999479
1965	7.699618854452637
1966	9.56895338175968
1967	11.40710049107545
1968	13.567198166191135
1969	15.461771292047775
1970	12.4526611767933
1971	14.373551035342857
1972	17.13438483904216
1973	20.129530134080994
1974	23.06873111682594
1975	27.56347429378735
1976	30.97209543061893
1977	35.78705844368378
1978	42.244527704810494
1979	49.7665367968702
1980	55.098931618826334
1981	58.413996263500486
1982	58.53700039771232
1983	58.862221449298126
1984	58.46570613429301
1985	53.52009594977068
1986	54.49017523360067
1987	55.2221687041998
1988	55.18666921750803
1989	54.41103167104372
1990	53.224273022325676
1991	53.169031496502605
1992	53.55993365958415
1993	53.79707176584552
1994	56.88025951083152
1995	58.209587335418696
1996	58.61554751121188
1997	62.01413452059239