Year	Years
1960	0.504
1961	1.403
1962	0.673
1963	1.951
1964	1.58
1965	2.221
1966	3.247
1967	3.977
1968	3.035
1969	3.578
1970	3.671
1971	3.04
1972	3.872
1973	3.773
1974	3.745
1975	3.465
1976	3.569
1977	3.007
1978	3.883
1979	4.066
1980	4.095
1981	4.469
1982	4.405
1983	3.651
1984	3.496
1985	4.589
1986	4.86
1987	4.67
1988	4.066
1989	3.817
1990	4.043
1991	3.241
1992	3.352
1993	3.928
1994	4.098
1995	3.576
1996	3.653
1997	4.1
1998	4.193
1999	4.452
2000	3.916
2001	3.986
2002	3.49
2003	3.451