Year	Years
1970	1.5
1971	1.6
1972	1.7
1973	1.8
1974	1.9
1975	2
1976	2.2
1977	2.3
1978	2.4
1979	2.6
1980	2.7
1981	2.8
1982	3
1983	3.1
1984	3.3
1985	3.5
1986	3.6
1987	3.8
1988	4
1989	4.2
1990	4.4
1991	4.6
1992	4.8
1993	5
1994	5.2
1995	5.4
1996	5.6
1997	5.8
1998	6
1999	6.2
2000	6.4
2001	6.6
2002	6.9
2003	7.1
2004	7.3
2005	7.5
2006	7.7
2007	7.9
2008	8.1
2009	8.3