Year	Years
1970	1.6
1971	1.6
1972	1.7
1973	1.8
1974	2
1975	2.1
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	3.4
1986	3.6
1987	3.7
1988	3.9
1989	4.1
1990	4.2
1991	4.4
1992	4.6
1993	4.8
1994	4.9
1995	5.1
1996	5.3
1997	5.5
1998	5.7
1999	5.9
2000	6
2001	6.2
2002	6.4
2003	6.6
2004	6.8
2005	7
2006	7.2
2007	7.4
2008	7.6
2009	7.7