Year	Years
1970	1.9
1971	2
1972	2.1
1973	2.1
1974	2.2
1975	2.3
1976	2.4
1977	2.5
1978	2.6
1979	2.7
1980	2.8
1981	2.9
1982	3
1983	3.2
1984	3.3
1985	3.4
1986	3.5
1987	3.6
1988	3.8
1989	3.9
1990	4
1991	4.1
1992	4.3
1993	4.4
1994	4.5
1995	4.7
1996	4.8
1997	4.9
1998	5.1
1999	5.2
2000	5.3
2001	5.5
2002	5.6
2003	5.7
2004	5.9
2005	6
2006	6.2
2007	6.3
2008	6.5
2009	6.6