Year	Years
1970	1.2
1971	1.2
1972	1.3
1973	1.3
1974	1.4
1975	1.5
1976	1.6
1977	1.6
1978	1.7
1979	1.8
1980	1.9
1981	2
1982	2
1983	2.1
1984	2.2
1985	2.3
1986	2.4
1987	2.5
1988	2.6
1989	2.7
1990	2.8
1991	2.9
1992	3
1993	3.1
1994	3.3
1995	3.4
1996	3.5
1997	3.6
1998	3.7
1999	3.8
2000	4
2001	4.1
2002	4.2
2003	4.4
2004	4.5
2005	4.6
2006	4.8
2007	4.9
2008	5.1
2009	5.2