Year	Percent
1991	41.12
1992	41.28
1993	41.56
1994	41.6
1995	41.43
1996	40.67
1997	40
1998	39.75
1999	39.86
2000	40.11
2001	40.27
2002	40.24
2003	40.67
2004	41.19
2005	41.46
2006	41.57
2007	41.47
2008	41.06
2009	40.5
2010	39.8
2011	38.14
2012	38.94
2013	39.84
2014	40.63
2015	41.29
2016	42.13
2017	42.04
2018	40.57
2019	38.16