Year	Percent
1989	37.08
1990	36.83
1991	37.04
1992	36
1993	33.27
1994	32.48
1995	34.23
1996	33.65
1997	33.43
1998	32.95
1999	31.64
2000	34.99
2001	33.75
2002	29.8
2003	30.7
2004	33.95
2005	34.05
2006	33.52
2007	35.1
2008	35.2
2009	31.39
2010	30.27
2011	32.41
2012	31.08
2013	30.24
2014	30.11
2015	30.6
2016	29.64
2017	29.84