Year	Percent
1986	19.5954
1987	17.0227
1988	15.6214
1989	13.1368
1990	11.985
1991	11.9533
1992	13.4752
1993	18.3924
1994	19.7998
1995	17.8646
1996	17.5669
1997	16.101
1998	13.6465
1999	10.7685
2000	9.4779
2001	7.3456
2002	7.8581
2003	8.2734
2004	8.3271
2005	7.1317
2006	6.3491
2007	6.4095
2008	10.0545
2009	17.6448
2010	19.5667
2011	21.044
2012	24.5801
2013	25.6011
2014	23.5977
2015	20.7742
2016	18.119
2017	15.6573