Year	Percent
1960	38.50067
1961	39.8053
1962	40.58455
1963	42.67004
1964	42.82932
1965	42.0068
1966	44.36964
1967	42.26756
1968	44.40566
1969	47.69101
1970	42.58821
1971	41.63788
1972	40.90158
1973	45.91505
1974	52.15384
1975	45.41277
1976	48.05509
1977	47.96437
1978	46.35198
1979	51.42976
1980	52.71189
1981	55.91779
1982	59.56633
1983	59.74347
1984	63.5456
1985	61.16011
1986	54.80869
1987	53.8203
1988	56.77116
1989	61.10786
1990	59.59832
1991	58.11103
1992	56.01988
1993	52.67886
1994	54.57307
1995	56.0237
1996	57.61731
1997	60.46992
1998	60.08723
1999	60.09852
2000	69.22148
2001	67.6741
2002	64.81011
2003	63.39422
2004	65.66786
2005	69.855
2006	71.98276
2007	73.67279
2008	79.21206
2009	67.04698
2010	74.65172
2011	81.11812
2012	81.68914
2013	80.48834
2014	82.03795
2015	79.43496
2016	81.60693
2017	84.34941