Year	Percent
1991	42.33
1992	42.26
1993	40.5
1994	40.47
1995	39.08
1996	40.03
1997	41.11
1998	41.06
1999	40.86
2000	40.89
2001	41.94
2002	43.22
2003	43.56
2004	43.93
2005	43.27
2006	42.62
2007	41.74
2008	41.03
2009	41.25
2010	41.35
2011	40.4
2012	40.13
2013	39.55
2014	39.66
2015	39.01
2016	38.75
2017	38.54
2018	38.34
2019	38.37