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	1.6
1982	1.7
1983	1.8
1984	1.8
1985	1.9
1986	2
1987	2
1988	2.1
1989	2.2
1990	2.2
1991	2.3
1992	2.4
1993	2.5
1994	2.5
1995	2.6
1996	2.7
1997	2.8
1998	2.9
1999	3
2000	3
2001	3.1
2002	3.2
2003	3.3
2004	3.4
2005	3.5
2006	3.6
2007	3.7
2008	3.8
2009	3.9