Year	Percent
1965	48.41448
1966	49.60581
1967	47.38341
1968	47.03607
1969	47.38613
1970	42.27879
1971	45.95473
1972	45.58165
1973	43.35224
1974	43.5928
1975	50.14132
1976	50.8937
1977	47.80613
1978	46.09765
1979	44.02812
1980	41.21967
1981	40.33823
1982	41.10285
1983	41.55631
1984	39.70819
1985	39.27615
1986	37.38043
1987	37.82868
1988	38.48661
1989	42.34781
1990	36.02188
1991	32.72253
1992	30.68395
1993	27.33874
1994	26.75458
1995	26.30112
1996	26.59253
1997	27.17912
1998	26.71206
1999	26.19338
2000	25.99095
2001	25.24351
2002	30.55778
2003	32.64509
2004	28.81692
2005	28.62631
2006	29.20328
2007	27.41524
2008	26.27246
2009	25.2842
2010	25.25878
2011	25.2127
2012	24.42906
2013	24.00588
2014	24.27739
2015	23.15306
2016	22.1875
2017	21.73665