Year	Years
1970	3
1971	3.1
1972	3.2
1973	3.3
1974	3.5
1975	3.6
1976	3.8
1977	3.9
1978	4.1
1979	4.2
1980	4.4
1981	4.6
1982	4.7
1983	4.9
1984	5.1
1985	5.3
1986	5.4
1987	5.6
1988	5.8
1989	6
1990	6.2
1991	6.4
1992	6.6
1993	6.8
1994	6.9
1995	7.1
1996	7.3
1997	7.5
1998	7.7
1999	7.8
2000	8
2001	8.2
2002	8.4
2003	8.5
2004	8.7
2005	8.8
2006	9
2007	9.2
2008	9.3
2009	9.5