Year	Years
1970	2
1971	2.1
1972	2.2
1973	2.3
1974	2.4
1975	2.5
1976	2.6
1977	2.6
1978	2.7
1979	2.8
1980	2.9
1981	3
1982	3.1
1983	3.3
1984	3.4
1985	3.5
1986	3.6
1987	3.7
1988	3.8
1989	3.9
1990	4.1
1991	4.2
1992	4.3
1993	4.4
1994	4.5
1995	4.7
1996	4.8
1997	4.9
1998	5
1999	5.1
2000	5.2
2001	5.3
2002	5.5
2003	5.6
2004	5.7
2005	5.8
2006	5.9
2007	6
2008	6.1
2009	6.2