Year	Years
1970	1.5
1971	1.6
1972	1.7
1973	1.7
1974	1.8
1975	1.9
1976	2
1977	2.1
1978	2.1
1979	2.2
1980	2.3
1981	2.4
1982	2.5
1983	2.6
1984	2.7
1985	2.7
1986	2.8
1987	2.9
1988	3
1989	3.1
1990	3.2
1991	3.4
1992	3.5
1993	3.6
1994	3.7
1995	3.8
1996	3.9
1997	4
1998	4.1
1999	4.2
2000	4.4
2001	4.5
2002	4.6
2003	4.7
2004	4.8
2005	5
2006	5.1
2007	5.2
2008	5.3
2009	5.4