Year	Percent
1960	0.29232
1961	0.31578
1962	0.34105
1963	0.36822
1964	0.39743
1965	0.42866
1966	0.4622
1967	0.51938
1968	0.58634
1969	0.66135
1970	0.74568
1971	0.84029
1972	0.94664
1973	1.06541
1974	1.19859
1975	1.34764
1976	1.51389
1977	1.69817
1978	1.81212
1979	1.90811
1980	2.01211
1981	2.12718
1982	2.25324
1983	2.38097
1984	2.49697
1985	2.59174
1986	2.66058
1987	2.71212
1988	2.72185
1989	2.74927
1990	2.81814
1991	2.93434
1992	3.09309
1993	3.28101
1994	3.47536
1995	3.6549
1996	3.81085
1997	3.94702
1998	4.07179
1999	4.1324
2000	4.1875
2001	4.25084
2002	4.31929
2003	4.39008
2004	4.4596
2005	4.52447
2006	4.58528
2007	4.64337
2008	4.70052
2009	4.75846
2010	4.8186
2011	4.88133
2012	4.94636
2013	5.01344
2014	5.08218
2015	5.15229
2016	5.22388
2017	5.29723