Year	Percent
1990	18.92
1991	18.47
1992	18.02
1993	17.57
1994	17.12
1995	16.67
1996	16.22
1997	15.77
1998	15.32
1999	14.87
2000	14.42
2001	13.97
2002	13.52
2003	13.07
2004	12.63
2005	12.18
2006	11.73
2007	11.28
2008	10.83
2009	10.38
2010	9.93
2011	9.48
2012	9.03
2013	8.58
2014	8.13
2015	7.68