Year	Percent
1991	55.95
1992	55.52
1993	53.14
1994	51.96
1995	51.43
1996	49.58
1997	48.38
1998	48.78
1999	47.45
2000	47.14
2001	46.96
2002	46.72
2003	46.54
2004	46.5
2005	46.64
2006	46.93
2007	47.35
2008	45.48
2009	43.8
2010	45.58
2011	47.02
2012	47.93
2013	48.79
2014	47.47
2015	46.48
2016	45.91
2017	45.62
2018	43.08
2019	42.97
2020	39.98