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	2.3
1979	2.4
1980	2.5
1981	2.7
1982	2.8
1983	3
1984	3.2
1985	3.3
1986	3.5
1987	3.7
1988	3.9
1989	4
1990	4.2
1991	4.4
1992	4.6
1993	4.8
1994	5
1995	5.1
1996	5.3
1997	5.5
1998	5.7
1999	5.9
2000	6.1
2001	6.3
2002	6.5
2003	6.7
2004	6.9
2005	7.1
2006	7.3
2007	7.5
2008	7.7
2009	7.9