Year	Percent
1991	33.4
1992	34.17
1993	35.12
1994	35.3
1995	35.12
1996	34.88
1997	34.33
1998	33.82
1999	32.42
2000	31.71
2001	31.63
2002	31.48
2003	31.57
2004	31.47
2005	31.89
2006	32.61
2007	35
2008	36.43
2009	38.89
2010	39.14
2011	38.17
2012	37.17
2013	36.34
2014	35.97
2015	35.39
2016	35.23
2017	35.1
2018	34.8
2019	34.62