Year	Percent
1960	23.02994
1961	21.92588
1962	22.07608
1963	24.71965
1964	24.74836
1965	26.81608
1966	30.07546
1967	30.54673
1968	31.61719
1969	30.86826
1970	34.10788
1971	30.50616
1972	28.20673
1973	33.09589
1974	44.07927
1975	39.67972
1976	38.16766
1977	39.26326
1978	40.29542
1979	41.37242
1980	44.0569
1981	37.70172
1982	28.05235
1983	29.23302
1984	32.02772
1985	29.86674
1986	28.30511
1987	25.82781
1988	28.9266
1989	34.34295
1990	39.94576
1991	37.57509
1992	36.2766
1993	43.704
1994	49.86141
1995	48.07903
1996	51.967
1997	51.81749
1998	54.07876
1999	55.97826
2000	66.41998
2001	64.56137
2002	65.26687
2003	68.15425
2004	77.03878
2005	77.48393
2006	77.07719
2007	81.56162
2008	84.42368
2009	57.37476
2010	63.68293
2011	70.95922
2012	70.28542
2013	68.36456
2014	65.41244
2015	62.09765
2016	57.87694
2017	58.85539