Year	Years
1970	1.4
1971	1.4
1972	1.5
1973	1.6
1974	1.7
1975	1.8
1976	1.9
1977	2
1978	2.1
1979	2.3
1980	2.4
1981	2.5
1982	2.6
1983	2.8
1984	2.9
1985	3
1986	3.2
1987	3.3
1988	3.4
1989	3.6
1990	3.7
1991	3.9
1992	4
1993	4.2
1994	4.3
1995	4.5
1996	4.6
1997	4.8
1998	5
1999	5.2
2000	5.3
2001	5.5
2002	5.7
2003	5.9
2004	6
2005	6.2
2006	6.4
2007	6.6
2008	6.8
2009	7