Year	Percent
1991	42.92
1992	42.14
1993	38.94
1994	36.71
1995	33.54
1996	27.81
1997	32.73
1998	34.32
1999	34.82
2000	35.21
2001	35.7
2002	36.19
2003	36.76
2004	37.44
2005	38.22
2006	39.16
2007	40.27
2008	41.44
2009	42.39
2010	42.91
2011	43.29
2012	43.46
2013	43.42
2014	43.26
2015	42.97
2016	42.93
2017	43.51
2018	41.62
2019	39.88