Year	Years
1970	0.7
1971	0.8
1972	0.8
1973	0.8
1974	0.9
1975	0.9
1976	1
1977	1
1978	1
1979	1.1
1980	1.1
1981	1.2
1982	1.2
1983	1.3
1984	1.3
1985	1.4
1986	1.4
1987	1.5
1988	1.5
1989	1.6
1990	1.7
1991	1.7
1992	1.8
1993	1.8
1994	1.9
1995	1.9
1996	2
1997	2
1998	2.1
1999	2.2
2000	2.2
2001	2.3
2002	2.3
2003	2.4
2004	2.4
2005	2.5
2006	2.6
2007	2.6
2008	2.7
2009	2.8