Year	Years
1970	1.5
1971	1.6
1972	1.6
1973	1.7
1974	1.8
1975	1.9
1976	1.9
1977	2
1978	2.1
1979	2.2
1980	2.3
1981	2.4
1982	2.5
1983	2.6
1984	2.7
1985	2.9
1986	3
1987	3.1
1988	3.2
1989	3.4
1990	3.5
1991	3.6
1992	3.7
1993	3.8
1994	4
1995	4.1
1996	4.2
1997	4.4
1998	4.5
1999	4.6
2000	4.7
2001	4.9
2002	5
2003	5.1
2004	5.2
2005	5.4
2006	5.5
2007	5.6
2008	5.8
2009	5.9