Year	Percent
1960	0.61223
1961	0.63585
1962	0.72626
1963	0.9128
1964	1.1475
1965	1.39858
1966	1.6589
1967	1.96753
1968	2.33439
1969	2.76818
1970	3.28355
1971	3.89508
1972	4.62206
1973	5.48205
1974	6.50423
1975	7.71762
1976	9.16075
1977	10.30562
1978	10.98657
1979	11.71237
1980	12.48712
1981	13.30888
1982	14.18636
1983	15.12321
1984	16.12808
1985	17.20096
1986	18.35277
1987	19.58596
1988	20.58953
1989	20.60186
1990	20.61892
1991	20.64121
1992	20.66735
1993	20.68637
1994	20.69092
1995	20.67467
1996	20.6369
1997	20.58041
1998	20.51708
1999	20.45768
2000	20.41062
2001	20.58806
2002	20.88814
2003	21.20014
2004	21.52255
2005	21.84929
2006	22.18578
2007	22.53089
2008	22.88116
2009	23.22644
2010	23.56758
2011	23.90197
2012	24.23494
2013	24.5699
2014	24.91986
2015	25.29196
2016	25.68871
2017	26.10864