Year	Percent
1991	41.15
1992	40.93
1993	40.9
1994	40.86
1995	40.83
1996	40.76
1997	40.71
1998	40.53
1999	40.31
2000	40.06
2001	39.95
2002	39.53
2003	39.2
2004	39
2005	39.31
2006	39.88
2007	40.06
2008	40.22
2009	40.19
2010	40.61
2011	38.37
2012	39.25
2013	39.67
2014	40.03
2015	39.95
2016	39.67
2017	39.6
2018	39.4
2019	39.41
2020	38.25