Year	Years
1970	1.6
1971	1.6
1972	1.7
1973	1.7
1974	1.8
1975	1.9
1976	1.9
1977	2
1978	2.1
1979	2.1
1980	2.2
1981	2.3
1982	2.4
1983	2.4
1984	2.5
1985	2.6
1986	2.7
1987	2.8
1988	2.9
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	3.8
1999	3.9
2000	4
2001	4.1
2002	4.2
2003	4.3
2004	4.4
2005	4.5
2006	4.6
2007	4.7
2008	4.8
2009	4.9