Year	Years
1970	1.4
1971	1.5
1972	1.6
1973	1.7
1974	1.8
1975	1.9
1976	2
1977	2.1
1978	2.2
1979	2.3
1980	2.4
1981	2.6
1982	2.7
1983	2.9
1984	3
1985	3.2
1986	3.3
1987	3.5
1988	3.7
1989	3.9
1990	4
1991	4.2
1992	4.4
1993	4.6
1994	4.8
1995	5
1996	5.2
1997	5.4
1998	5.7
1999	5.9
2000	6.1
2001	6.3
2002	6.5
2003	6.8
2004	7
2005	7.2
2006	7.4
2007	7.7
2008	7.9
2009	8.1