Year	Percent
1990	26.33
1991	26.11
1992	25.9
1993	25.69
1994	25.47
1995	25.26
1996	25.04
1997	24.83
1998	24.61
1999	24.4
2000	24.18
2001	23.86
2002	23.54
2003	23.21
2004	22.89
2005	22.57
2006	22.25
2007	21.92
2008	21.6
2009	21.28
2010	20.96
2011	20.74
2012	20.53
2013	20.31
2014	20.1
2015	19.88