Year	Years
1970	2.1
1971	2.2
1972	2.3
1973	2.4
1974	2.5
1975	2.6
1976	2.7
1977	2.8
1978	2.9
1979	3
1980	3.1
1981	3.2
1982	3.3
1983	3.5
1984	3.6
1985	3.7
1986	3.8
1987	4
1988	4.1
1989	4.2
1990	4.4
1991	4.5
1992	4.6
1993	4.8
1994	4.9
1995	5.1
1996	5.2
1997	5.3
1998	5.5
1999	5.6
2000	5.8
2001	5.9
2002	6.1
2003	6.2
2004	6.4
2005	6.5
2006	6.7
2007	6.8
2008	7
2009	7.2