Year	Years
1970	2.1
1971	2.17
1972	2.23
1973	2.3
1974	2.37
1975	2.44
1976	2.52
1977	2.59
1978	2.67
1979	2.75
1980	2.84
1981	2.92
1982	3.01
1983	3.1
1984	3.19
1985	3.28
1986	3.38
1987	3.48
1988	3.58
1989	3.68
1990	3.79
1991	3.9
1992	4.01
1993	4.12
1994	4.24
1995	4.36
1996	4.49
1997	4.62
1998	4.76
1999	4.9
2000	5.04
2001	5.18
2002	5.32
2003	5.46
2004	5.61
2005	5.75
2006	5.9
2007	6.05
2008	6.2
2009	6.36
2010	6.51
2011	6.67
2012	6.82
2013	6.98
2014	7.14
2015	7.3