Year	Percent
1990	28.53
1991	28.02
1992	27.49
1993	26.98
1994	26.44
1995	25.94
1996	25.43
1997	24.89
1998	24.39
1999	23.85
2000	23.34
2001	22.83
2002	22.3
2003	21.79
2004	21.26
2005	20.75
2006	20.24
2007	19.71
2008	19.2
2009	18.66
2010	18.16
2011	17.65
2012	17.11
2013	16.6
2014	16.07
2015	15.56