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	1.4
1979	1.5
1980	1.5
1981	1.6
1982	1.7
1983	1.7
1984	1.8
1985	1.9
1986	1.9
1987	2
1988	2
1989	2.1
1990	2.2
1991	2.2
1992	2.3
1993	2.4
1994	2.5
1995	2.5
1996	2.6
1997	2.7
1998	2.7
1999	2.8
2000	2.9
2001	3
2002	3.1
2003	3.1
2004	3.2
2005	3.3
2006	3.4
2007	3.5
2008	3.5
2009	3.6