Year	Years
1970	1.3
1971	1.3
1972	1.4
1973	1.5
1974	1.5
1975	1.6
1976	1.7
1977	1.7
1978	1.8
1979	1.9
1980	2
1981	2.1
1982	2.1
1983	2.2
1984	2.3
1985	2.4
1986	2.5
1987	2.6
1988	2.7
1989	2.8
1990	2.9
1991	3
1992	3.1
1993	3.2
1994	3.4
1995	3.5
1996	3.6
1997	3.7
1998	3.8
1999	4
2000	4.1
2001	4.2
2002	4.3
2003	4.5
2004	4.6
2005	4.7
2006	4.8
2007	5
2008	5.1
2009	5.3