Year	Years
1970	1.1
1971	1.1
1972	1.2
1973	1.2
1974	1.3
1975	1.3
1976	1.4
1977	1.4
1978	1.5
1979	1.5
1980	1.6
1981	1.6
1982	1.7
1983	1.8
1984	1.8
1985	1.9
1986	1.9
1987	2
1988	2
1989	2.1
1990	2.2
1991	2.2
1992	2.3
1993	2.3
1994	2.4
1995	2.5
1996	2.5
1997	2.6
1998	2.7
1999	2.7
2000	2.8
2001	2.9
2002	3
2003	3
2004	3.1
2005	3.2
2006	3.3
2007	3.4
2008	3.4
2009	3.5