Year	Percent
1991	40.52
1992	40.79
1993	41.1
1994	41.29
1995	41.51
1996	41.55
1997	41.56
1998	41.53
1999	41.5
2000	40.65
2001	39.84
2002	39.04
2003	38.3
2004	37.63
2005	37.01
2006	36.46
2007	35.94
2008	35.42
2009	34.78
2010	34.31
2011	33.58
2012	32.93
2013	32.36
2014	31.87
2015	32.31
2016	32.62
2017	32.92
2018	33.17
2019	33.39
2020	33.02