Year	Years
1970	2.03
1971	2.1
1972	2.17
1973	2.24
1974	2.31
1975	2.39
1976	2.47
1977	2.55
1978	2.64
1979	2.73
1980	2.82
1981	2.91
1982	3.01
1983	3.1
1984	3.21
1985	3.31
1986	3.42
1987	3.53
1988	3.64
1989	3.76
1990	3.88
1991	4
1992	4.12
1993	4.24
1994	4.37
1995	4.49
1996	4.6
1997	4.71
1998	4.83
1999	4.95
2000	5.07
2001	5.19
2002	5.32
2003	5.45
2004	5.58
2005	5.71
2006	5.85
2007	5.99
2008	6.13
2009	6.27
2010	6.41
2011	6.56
2012	6.71
2013	6.86
2014	7.01
2015	7.16