Year	Percent
1989	8.28
1990	6.68
1991	8.81
1992	8.03
1993	11.84
1994	12.64
1995	15.13
1996	14.94
1997	14.16
1999	37.45
2000	36.7
2001	40.24
2002	38.81
2003	33.87
2004	33.87
2005	36.82
2006	38.66
2007	34.36
2008	30.66
2009	29.34
2011	30.81
2012	23.11
2013	26.24
2014	29.47
2015	25.05
2016	25.7
2017	24.91