Year	Years
1970	1.8
1971	1.8
1972	1.9
1973	2
1974	2
1975	2.1
1976	2.2
1977	2.2
1978	2.3
1979	2.4
1980	2.5
1981	2.5
1982	2.6
1983	2.7
1984	2.8
1985	2.9
1986	2.9
1987	3
1988	3.1
1989	3.2
1990	3.3
1991	3.4
1992	3.4
1993	3.5
1994	3.6
1995	3.7
1996	3.8
1997	3.9
1998	4
1999	4.1
2000	4.2
2001	4.3
2002	4.3
2003	4.4
2004	4.5
2005	4.6
2006	4.7
2007	4.8
2008	4.9
2009	5