Year	Years
1970	1.5
1971	1.6
1972	1.6
1973	1.7
1974	1.8
1975	1.9
1976	1.9
1977	2
1978	2.1
1979	2.2
1980	2.3
1981	2.4
1982	2.5
1983	2.5
1984	2.6
1985	2.7
1986	2.9
1987	3
1988	3.1
1989	3.2
1990	3.3
1991	3.4
1992	3.5
1993	3.7
1994	3.8
1995	3.9
1996	4
1997	4.1
1998	4.2
1999	4.4
2000	4.5
2001	4.6
2002	4.7
2003	4.8
2004	5
2005	5.1
2006	5.2
2007	5.3
2008	5.5
2009	5.6