Year	Percent
1987	26.71
1988	29
1989	28.85
1990	26.98
1991	24.84
1992	25.47
1993	21.45
1994	21.61
1995	18.5
1996	16.3
1997	18.09
1998	18.41
1999	16.47
2000	16.42
2001	15.58
2002	15.92
2003	15.96
2004	14.66
2005	13.54
2006	13.88
2007	14.05
2008	14.68
2009	13.57
2010	14.18
2011	16.26
2012	17
2013	12.04
2014	11.78
2015	11.5
2016	11.37