Year	Percent
1960	2.02536
1961	2.15994
1962	2.30117
1963	2.44972
1964	2.60715
1965	2.77381
1966	2.95118
1967	3.13996
1968	3.34338
1969	3.56381
1970	3.59765
1971	3.60755
1972	3.62283
1973	3.64045
1974	3.6576
1975	3.6719
1976	3.68276
1977	3.69031
1978	3.69599
1979	3.701
1980	3.73391
1981	3.80074
1982	3.86876
1983	3.93603
1984	4.00062
1985	4.06049
1986	4.11609
1987	4.16835
1988	4.21976
1989	4.27227
1990	4.32861
1991	4.39166
1992	4.46172
1993	4.5348
1994	4.61195
1995	4.69278
1996	4.77795
1997	4.86594
1998	4.9556
1999	5.04392
2000	5.12946
2001	5.21069
2002	5.28947
2003	5.36669
2004	5.44445
2005	5.52288
2006	5.60345
2007	5.68564
2008	5.76998
2009	5.85532
2010	5.94295
2011	6.03268
2012	6.12524
2013	6.21974
2014	6.31776
2015	6.41921
2016	6.52428
2017	6.63309