Year	Percent
1990	43.12
1992	39.67
1994	38.94
1995	39.83
1996	37.94
1997	37.48
1998	38.07
1999	38.32
2000	39.2
2001	36.46
2002	36.58
2003	34.01
2004	33.48
2005	32.4
2006	32.05
2007	40.23
2008	31.5
2009	29.53
2010	28.54
2011	27.92
2012	27.75
2013	33.69
2014	33.38
2015	32.55
2016	33.19
2017	31.41