Year	Years
1970	1.3
1971	1.4
1972	1.5
1973	1.6
1974	1.7
1975	1.7
1976	1.8
1977	1.9
1978	2
1979	2.2
1980	2.3
1981	2.4
1982	2.5
1983	2.6
1984	2.8
1985	2.9
1986	3
1987	3.2
1988	3.3
1989	3.5
1990	3.7
1991	3.8
1992	4
1993	4.2
1994	4.3
1995	4.5
1996	4.7
1997	4.9
1998	5.1
1999	5.3
2000	5.5
2001	5.7
2002	5.9
2003	6.1
2004	6.3
2005	6.5
2006	6.7
2007	6.9
2008	7.1
2009	7.3