Year	Percent
1987	17.98
1988	17.75
1989	18.7
1990	19.19
1991	18.48
1993	19.53
1995	17.02
1996	17.26
1998	15.37
1999	13.15
2000	11.94
2002	11.86
2005	8.21
2006	6.64
2007	6.39
2008	4.9
2009	5.01
2010	3.4571
2011	3.2847
2012	3.9176
2013	2.7703
2014	2.3409
2015	2.5647
2016	2.6981