Year	Years
1970	1.3
1971	1.4
1972	1.4
1973	1.5
1974	1.6
1975	1.7
1976	1.7
1977	1.8
1978	1.9
1979	2
1980	2
1981	2.1
1982	2.2
1983	2.3
1984	2.4
1985	2.5
1986	2.6
1987	2.7
1988	2.8
1989	2.9
1990	3
1991	3.1
1992	3.2
1993	3.3
1994	3.4
1995	3.5
1996	3.6
1997	3.7
1998	3.9
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	5.2