Year	Percent
1990	60.62
1991	60.47
1992	60.33
1993	60.14
1994	59.97
1995	59.77
1996	59.62
1997	59.49
1998	59.31
1999	59.11
2000	58.89
2001	58.07
2002	57.24
2003	56.41
2004	55.57
2005	54.73
2006	53.89
2007	52.56
2008	51.22
2009	49.88
2010	48.54
2011	47.2
2012	45.87
2013	44.53
2014	43.19
2015	41.86
2016	41.73
2017	41.44
2018	41.2
2019	40.93