Year	Percent
1990	25.03
1991	24.81
1992	24.59
1993	24.37
1994	24.15
1995	23.93
1996	23.71
1997	23.49
1998	23.27
1999	23.06
2000	22.84
2001	22.62
2002	22.4
2003	22.18
2004	21.96
2005	21.74
2006	21.52
2007	21.3
2008	21.09
2009	20.87
2010	20.65
2011	20.43
2012	20.21
2013	19.99
2014	19.77
2015	19.55