Year	Years
1970	0.8
1971	0.8
1972	0.9
1973	0.9
1974	1
1975	1
1976	1.1
1977	1.1
1978	1.2
1979	1.3
1980	1.4
1981	1.4
1982	1.5
1983	1.6
1984	1.7
1985	1.8
1986	1.9
1987	2
1988	2.1
1989	2.2
1990	2.3
1991	2.4
1992	2.6
1993	2.7
1994	2.8
1995	2.9
1996	3.1
1997	3.2
1998	3.4
1999	3.5
2000	3.7
2001	3.8
2002	4
2003	4.1
2004	4.3
2005	4.4
2006	4.6
2007	4.8
2008	5
2009	5.1