Year	Years
1970	1.5
1971	1.6
1972	1.7
1973	1.8
1974	1.9
1975	2
1976	2.1
1977	2.2
1978	2.3
1979	2.4
1980	2.5
1981	2.6
1982	2.7
1983	2.8
1984	2.9
1985	3
1986	3.2
1987	3.3
1988	3.4
1989	3.5
1990	3.6
1991	3.7
1992	3.9
1993	4
1994	4.1
1995	4.3
1996	4.4
1997	4.5
1998	4.7
1999	4.8
2000	5
2001	5.1
2002	5.2
2003	5.4
2004	5.5
2005	5.7
2006	5.8
2007	6
2008	6.2
2009	6.3