Year	Years
1970	2.2
1971	2.3
1972	2.4
1973	2.4
1974	2.5
1975	2.6
1976	2.7
1977	2.8
1978	2.9
1979	3
1980	3.2
1981	3.3
1982	3.4
1983	3.5
1984	3.6
1985	3.7
1986	3.9
1987	4
1988	4.1
1989	4.2
1990	4.3
1991	4.4
1992	4.5
1993	4.6
1994	4.7
1995	4.8
1996	4.9
1997	5
1998	5.1
1999	5.2
2000	5.3
2001	5.4
2002	5.5
2003	5.6
2004	5.7
2005	5.8
2006	5.9
2007	5.9
2008	6
2009	6.1