Year	Years
1970	2.2
1971	2.3
1972	2.4
1973	2.5
1974	2.6
1975	2.7
1976	2.8
1977	2.9
1978	3
1979	3.1
1980	3.2
1981	3.3
1982	3.4
1983	3.5
1984	3.6
1985	3.7
1986	3.8
1987	3.9
1988	4
1989	4
1990	4.1
1991	4.2
1992	4.3
1993	4.4
1994	4.5
1995	4.6
1996	4.7
1997	4.9
1998	5
1999	5.1
2000	5.2
2001	5.3
2002	5.4
2003	5.5
2004	5.6
2005	5.7
2006	5.8
2007	5.9
2008	6
2009	6.1