Year	Percent
1965	21.34524
1966	19.89652
1967	17.76131
1968	17.00004
1969	17.51297
1970	18.75163
1971	18.89173
1972	19.13331
1973	19.16034
1974	37.24361
1975	41.28018
1976	33.99733
1977	33.19751
1978	37.01889
1979	48.3353
1980	42.86598
1981	48.80485
1982	41.93254
1983	36.42946
1984	35.81252
1985	32.04153
1986	25.59443
1987	22.76629
1988	35.16113
1989	32.3514
1990	32.71329
1991	35.79569
1992	30.91301
1993	30.09021
1994	28.05714
1995	27.69608
1996	26.19878
1997	24.89658
1998	25.71329
1999	23.30949
2000	22.81682
2001	22.33064
2002	22.67089
2003	24.38323
2004	29.58994
2005	32.6091
2006	31.56872
2007	34.82814
2008	38.63763
2009	31.59662
2010	26.5871
2011	24.68821
2012	24.3148
2013	23.35519
2014	22.67606
2015	21.6621
2016	19.67594
2017	28.48703