Year	Percent
1990	18.19
1991	17.98
1992	17.76
1993	17.54
1994	17.33
1995	17.11
1996	16.89
1997	16.67
1998	16.46
1999	16.24
2000	16.02
2001	15.8
2002	15.58
2003	15.36
2004	15.14
2005	14.91
2006	14.7
2007	14.49
2008	14.28
2009	14.06
2010	13.85
2011	13.64
2012	13.43
2013	13.21
2014	13
2015	12.79