Year	Percent
1989	18.3595
1990	18.00284
1991	13.20865
1992	11.3778
1993	9.67474
1994	7.87061
1995	10.80645
1996	12.84632
1997	14.53196
1998	13.76343
1999	14.06399
2000	14.17756
2001	15.60492
2002	16.09864
2003	16.73658
2004	36.22349
2005	37.81746
2006	36.67904
2007	38.22672
2008	38.97208
2009	33.69896
2010	35.79364
2011	36.94092
2012	34.09319
2013	31.81945
2014	27.59761
2015	26.90066
2016	25.49448
2017	23.60267