Year	Percent
1991	54.84
1992	55.67
1993	55.03
1994	55.92
1995	56.5
1996	56.47
1997	56.46
1998	56.45
1999	55.38
2000	54.38
2001	54.14
2002	52.18
2003	51.88
2004	54.11
2005	54.97
2006	56.76
2007	58.83
2008	60.23
2009	60.68
2010	60.79
2011	61.71
2012	61.17
2013	60.7
2014	61.11
2015	60.1
2016	59.61
2017	59.15
2018	58.57
2019	57.93
2020	53.23