Year	Percent
1991	42.89
1992	44.8
1993	45.01
1994	46.35
1995	46.22
1996	44.28
1997	43.24
1998	42.02
1999	42.11
2000	42.29
2001	41.61
2002	38.25
2003	38.76
2004	38.48
2005	39.33
2006	39.79
2007	39.86
2008	39.85
2009	39.81
2010	39.39
2011	39.07
2012	36.87
2013	40.92
2014	38.1
2015	36.77
2016	35.21
2017	33.68
2018	32.15
2019	31.79