Year	Years
1970	1.5
1971	1.6
1972	1.7
1973	1.8
1974	1.9
1975	2
1976	2.1
1977	2.2
1978	2.3
1979	2.4
1980	2.6
1981	2.7
1982	2.8
1983	2.9
1984	3.1
1985	3.2
1986	3.3
1987	3.5
1988	3.6
1989	3.7
1990	3.9
1991	4
1992	4.1
1993	4.3
1994	4.4
1995	4.6
1996	4.8
1997	4.9
1998	5.1
1999	5.2
2000	5.4
2001	5.6
2002	5.7
2003	5.9
2004	6.1
2005	6.2
2006	6.4
2007	6.6
2008	6.8
2009	6.9