Year	Percent
1990	52.03
1991	53.6
1992	51.61
1993	52.38
1994	52.13
1995	51.45
1996	51.19
1997	44.96
1998	43.12
1999	43.22
2000	42.19
2001	41.48
2002	39.82
2003	39.92
2004	37.56
2005	40.04
2006	37.55
2007	37.44
2008	36.06
2009	34.49
2010	32.88
2011	33.87
2012	34.57
2013	35.02
2014	35.28
2015	35.51
2016	36.11
2017	36.65
2018	37.55
2019	38.7