Year	Percent
1991	43.22
1992	42.6
1993	42.12
1994	41.96
1995	41.65
1996	41.31
1997	40.85
1998	40.48
1999	40.13
2000	39.91
2001	37.77
2002	37.97
2003	35.82
2004	36.68
2005	36.14
2006	37.72
2007	37
2008	38.47
2009	33.16
2010	35.05
2011	35.14
2012	35.12
2013	33.89
2014	36.11
2015	37.49
2016	37.76
2017	38.85
2018	39.34
2019	39.61