Year	Percent
1991	52.7
1992	53.52
1993	55.06
1994	50.37
1995	47.41
1996	44.79
1997	44.28
1998	44.13
1999	43.18
2000	42.55
2001	43.16
2002	42.78
2003	43.47
2004	42.65
2005	42.53
2006	42.42
2007	42.54
2008	42.76
2009	42.99
2010	42.72
2011	42.34
2012	41.92
2013	41.13
2014	43.3
2015	45.17
2016	42.85
2017	40.21
2018	38.97
2019	37.41