Year	Percent
1966	33.42468
1967	35.33676
1968	37.52142
1969	34.63809
1970	32.66411
1971	31.03331
1972	31.41965
1973	37.22799
1974	50.98862
1975	49.69906
1976	49.07315
1977	48.32599
1978	42.00547
1979	45.09768
1980	48.14914
1981	40.75681
1982	31.27246
1983	31.68679
1984	34.63716
1985	33.97488
1986	30.96466
1987	33.4553
1988	32.85623
1989	36.79747
1990	38.20279
1991	35.3107
1992	32.82882
1993	31.89671
1994	37.66823
1995	35.71525
1996	36.06281
1997	33.32441
1998	27.60173
1999	30.47977
2000	38.3454
2001	35.69205
2002	34.21407
2003	42.9347
2004	46.13708
2005	51.36112
2006	52.57597
2007	50.27356
2008	54.84879
2009	40.35201
2010	45.87146
2011	50.44249
2012	50.10941
2013	47.97559
2014	47.52201
2015	37.03729
2016	35.42801
2017	38.24753