Year	Percent
1986	44.1903
1987	38.4353
1988	35.1894
1989	27.5095
1990	25.6631
1991	25.2269
1992	27.8037
1993	38.8773
1994	41.1294
1995	36.3675
1996	36.5111
1997	33.6454
1998	29.2664
1999	22.9238
2000	19.628
2001	16.412
2002	16.8192
2003	19.1585
2004	19.4437
2005	16.7167
2006	14.9918
2007	15.2233
2008	23.5855
2009	39.0632
2010	43.0803
2011	48.1525
2012	54.1239
2013	56.2229
2014	53.4288
2015	48.6465
2016	44.0402
2017	39.5491