Year	Years
1970	1.9
1971	2
1972	2.1
1973	2.2
1974	2.3
1975	2.4
1976	2.5
1977	2.7
1978	2.8
1979	2.9
1980	3
1981	3.1
1982	3.3
1983	3.4
1984	3.5
1985	3.7
1986	3.8
1987	4
1988	4.1
1989	4.2
1990	4.4
1991	4.5
1992	4.7
1993	4.8
1994	5
1995	5.1
1996	5.3
1997	5.4
1998	5.6
1999	5.7
2000	5.9
2001	6.1
2002	6.2
2003	6.4
2004	6.5
2005	6.7
2006	6.8
2007	7
2008	7.2
2009	7.3