Year	Percent
1991	42.55
1992	41.68
1993	41.05
1994	39.67
1995	37.89
1996	36.61
1997	37.83
1998	36.59
1999	37.95
2000	39.77
2001	41.48
2002	40.88
2003	40.85
2004	40.85
2005	40.81
2006	41.63
2007	41.84
2008	41.6
2009	40.92
2010	40.53
2011	40.23
2012	39.95
2013	39.69
2014	39.98
2015	39.81
2016	40.79
2017	42.09
2018	42.1
2019	42.15