Year	Percent
1983	15.2934
1984	16.6527
1985	17.9383
1986	18.6067
1987	17.9218
1988	16.9028
1989	15.7378
1990	14.2406
1991	15.4643
1992	13.9106
1993	14.0936
1994	13.2471
1995	10.7223
1996	10.6177
1997	9.1762
1998	6.5604
1999	4.9169
2000	3.7135
2001	3.0786
2002	3.2129
2003	3.4873
2004	3.2268
2005	3.2385
2006	3.5432
2007	4.3896
2008	4.8835
2009	8.4097
2010	10.2122
2011	11.6152
2012	11.7638
2013	11.285
2014	9.9648
2015	8.2415
2016	7.0586
2017	5.4411