Year	Years
1970	1
1971	1.1
1972	1.1
1973	1.2
1974	1.2
1975	1.3
1976	1.3
1977	1.4
1978	1.5
1979	1.5
1980	1.6
1981	1.7
1982	1.7
1983	1.8
1984	1.9
1985	2
1986	2
1987	2.1
1988	2.2
1989	2.3
1990	2.4
1991	2.4
1992	2.5
1993	2.6
1994	2.7
1995	2.8
1996	2.9
1997	3
1998	3.1
1999	3.2
2000	3.3
2001	3.4
2002	3.5
2003	3.6
2004	3.7
2005	3.8
2006	3.9
2007	4
2008	4.1
2009	4.2