Year	Years
1970	1.5
1971	1.6
1972	1.7
1973	1.8
1974	1.9
1975	2
1976	2.1
1977	2.3
1978	2.4
1979	2.5
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	4.1
1990	4.3
1991	4.5
1992	4.6
1993	4.8
1994	5
1995	5.2
1996	5.4
1997	5.6
1998	5.8
1999	6
2000	6.2
2001	6.3
2002	6.5
2003	6.7
2004	6.9
2005	7.1
2006	7.4
2007	7.6
2008	7.8
2009	7.9