Year	Percent
1991	52.37
1992	51.64
1993	50.77
1994	49.93
1995	49.15
1996	48.53
1997	48.09
1998	47.69
1999	47.23
2000	45.64
2001	43.97
2002	42.22
2003	40.46
2004	38.69
2005	36.93
2006	37.61
2007	38.32
2008	39
2009	39.41
2010	39.82
2011	40.19
2012	40.47
2013	40.71
2014	41.05
2015	41.48
2016	42.01
2017	41.14
2018	40.31
2019	39.44