Year	Percent
1991	39.2
1992	38.56
1993	37.94
1994	37.29
1995	36.6
1996	36.74
1997	36.77
1998	36.77
1999	36.87
2000	37.17
2001	37.23
2002	37.31
2003	37.33
2004	37.25
2005	37.03
2006	36.66
2007	36.22
2008	35.67
2009	34.36
2010	37.33
2011	40.28
2012	43.23
2013	46.16
2014	49.13
2015	47.85
2016	47.53
2017	48.8
2018	49.25
2019	48.87