Year	Percent
1990	21.98
1991	22.14
1992	22.3
1993	22.46
1994	22.62
1995	22.78
1996	22.93
1997	23.09
1998	23.25
1999	23.41
2000	23.57
2001	23.6
2002	23.63
2003	23.66
2004	23.69
2005	23.72
2006	23.57
2007	23.41
2008	23.25
2009	23.1
2010	22.94
2011	23.74
2012	24.55
2013	25.35
2014	26.16
2015	26.96