Year	Years
1970	1.7
1971	1.7
1972	1.8
1973	1.9
1974	2
1975	2.1
1976	2.2
1977	2.3
1978	2.4
1979	2.4
1980	2.5
1981	2.6
1982	2.7
1983	2.9
1984	3
1985	3.1
1986	3.2
1987	3.3
1988	3.4
1989	3.5
1990	3.6
1991	3.7
1992	3.8
1993	3.9
1994	4
1995	4.1
1996	4.2
1997	4.3
1998	4.5
1999	4.6
2000	4.7
2001	4.8
2002	5
2003	5.1
2004	5.2
2005	5.3
2006	5.5
2007	5.6
2008	5.7
2009	5.9