Year	Years
1970	2.3
1971	2.4
1972	2.5
1973	2.7
1974	2.8
1975	2.9
1976	3.1
1977	3.2
1978	3.4
1979	3.5
1980	3.7
1981	3.8
1982	4
1983	4.2
1984	4.3
1985	4.5
1986	4.7
1987	4.9
1988	5.1
1989	5.3
1990	5.5
1991	5.6
1992	5.8
1993	6
1994	6.2
1995	6.4
1996	6.6
1997	6.8
1998	7
1999	7.2
2000	7.4
2001	7.6
2002	7.8
2003	7.9
2004	8.1
2005	8.3
2006	8.5
2007	8.7
2008	8.9
2009	9