Year	Years
1961	4.301
1962	3.963
1963	4.008
1964	4.361
1965	4.719
1966	5.2
1967	5.59
1968	5.924
1969	6.176
1970	6.776
1971	7.446
1972	8.092
1973	8.539
1974	7.471
1975	6.968
1976	7.503
1977	7.526
1978	8.005
1979	7.951
1980	7.545
1981	6.935
1982	6.011
1983	5.642
1984	6.671
1985	6.738
1986	6.64
1987	6.964
1988	6.481
1989	6.601
1990	6.619
1991	6.817
1992	7.266
1993	7.186
1994	6.906
1995	7.075
1996	6.567
1997	5.977
1998	5.661
1999	5.439
2000	5.45
2001	4.567
2002	4.264
2003	3.923
2004	3.791