Year	Percent
1991	38.09
1992	37.69
1993	38.96
1994	39.63
1995	39.53
1996	40.49
1997	41.23
1998	41.39
1999	42.04
2000	41.67
2001	41.32
2002	41.34
2003	41.47
2004	42.04
2005	41.91
2006	42.31
2007	41.73
2008	40.62
2009	38.46
2010	37.43
2011	37.01
2012	36.93
2013	36.37
2014	35.85
2015	35.9
2016	35.87
2017	36.1
2018	36.48
2019	36.5
2020	33.7