Year	Percent
1990	40.22
1991	39.84
1992	38.77
1993	38.02
1994	35.88
1995	33.96
1996	32.55
1997	30.01
1998	29.13
1999	29
2000	29.24
2001	30.18
2002	30.17
2003	30.23
2004	29.63
2005	29.56
2006	29.25
2007	29.16
2008	28.97
2009	27.46
2010	27.74
2011	27.45
2012	27.77
2013	27.73
2014	27.52
2015	27.18
2016	26.95
2017	26.97