Year	Percent
1975	25.4643
1976	27.64019
1977	31.53314
1978	31.31213
1979	28.09722
1980	26.84579
1981	31.08839
1982	36.20758
1983	37.86522
1984	36.34681
1985	37.82203
1986	46.6611
1987	44.17567
1988	45.78803
1989	43.73005
1990	40.03922
1991	51.92393
1992	43.32336
1993	47.03918
1994	51.9092
1995	52.66776
1996	51.84057
1997	52.56757
1998	57.79558
1999	55.64609
2000	49.22034
2001	48.08546
2002	50.25093
2003	48.9513
2004	46.65629
2005	42.96097
2006	41.00264
2007	44.1831
2008	41.15472
2009	46.91816
2010	38.71856
2011	33.55831
2012	34.21476
2013	36.79186
2014	38.80533
2015	46.50147
2016	48.79085
2017	46.85571