Year	Percent
1991	54.49
1992	53.15
1993	51.34
1994	49.69
1995	47.41
1996	47.01
1997	46.49
1998	43.56
1999	41.31
2000	41.65
2001	39.93
2002	38.53
2003	38.4
2004	39.29
2005	38.82
2006	38.4
2007	39.15
2008	37.6
2009	34.24
2010	31.5
2011	32.95
2012	33.73
2013	35.55
2014	35.37
2015	36.15
2016	36.71
2017	37.34
2018	37.7
2019	38.02