Year	Percent
1960	18.74014
1961	20.02509
1962	21.36437
1963	22.14349
1964	22.27928
1965	22.42405
1966	22.58595
1967	22.76032
1968	22.9426
1969	23.11405
1970	23.27254
1971	23.42257
1972	23.57043
1973	23.71982
1974	23.88348
1975	24.06628
1976	24.27066
1977	24.49026
1978	24.72502
1979	24.90252
1980	25.01453
1981	25.13397
1982	25.26552
1983	25.39622
1984	25.51203
1985	25.60408
1986	25.6682
1987	25.71903
1988	25.79946
1989	25.93979
1990	26.17464
1991	26.53349
1992	27.00274
1993	27.55315
1994	28.14769
1995	28.7536
1996	29.36293
1997	29.97699
1998	30.59722
1999	31.22359
2000	31.91418
2001	32.89796
2002	33.8954
2003	34.90179
2004	35.91623
2005	36.93038
2006	37.9515
2007	38.97526
2008	39.99291
2009	40.98368
2010	41.9457
2011	42.77277
2012	43.51545
2013	44.24861
2014	45.01422
2015	45.83703
2016	46.7299
2017	47.68392