Year	Percent
1991	37
1992	36.43
1993	35.9
1994	35.75
1995	35.29
1996	34.99
1997	34.69
1998	34.3
1999	33.9
2000	33.66
2001	33.48
2002	33.33
2003	33.19
2004	33.3
2005	33.53
2006	33.31
2007	33.1
2008	32.8
2009	31.81
2010	31.31
2011	31.37
2012	31.29
2013	31.03
2014	30.77
2015	30.39
2016	30.56
2017	30.95
2018	31.31
2019	31.61