Year	Years
1970	1.6
1971	1.6
1972	1.7
1973	1.8
1974	1.8
1975	1.9
1976	2
1977	2.1
1978	2.1
1979	2.2
1980	2.3
1981	2.4
1982	2.4
1983	2.5
1984	2.6
1985	2.7
1986	2.8
1987	2.9
1988	3
1989	3.1
1990	3.2
1991	3.3
1992	3.4
1993	3.5
1994	3.6
1995	3.7
1996	3.8
1997	3.9
1998	4
1999	4.1
2000	4.2
2001	4.3
2002	4.5
2003	4.6
2004	4.7
2005	4.8
2006	4.9
2007	5
2008	5.2
2009	5.3