Year	Years
1970	2.1
1971	2.16
1972	2.23
1973	2.3
1974	2.37
1975	2.45
1976	2.53
1977	2.61
1978	2.69
1979	2.77
1980	2.86
1981	2.95
1982	3.04
1983	3.13
1984	3.23
1985	3.33
1986	3.43
1987	3.53
1988	3.64
1989	3.75
1990	3.86
1991	3.98
1992	4.1
1993	4.22
1994	4.35
1995	4.48
1996	4.6
1997	4.73
1998	4.85
1999	4.99
2000	5.12
2001	5.25
2002	5.39
2003	5.52
2004	5.66
2005	5.8
2006	5.94
2007	6.09
2008	6.23
2009	6.38
2010	6.53
2011	6.68
2012	6.83
2013	6.99
2014	7.14
2015	7.3