Year	Percent
1990	23.78
1991	23.34
1992	22.89
1993	22.45
1994	22.01
1995	21.57
1996	21.13
1997	20.69
1998	20.25
1999	19.8
2000	19.36
2001	18.92
2002	18.48
2003	18.04
2004	17.6
2005	17.16
2006	16.48
2007	15.81
2008	15.13
2009	14.45
2010	13.73
2011	13.06
2012	12.38
2013	11.71
2014	11.03
2015	10.36