Year	Percent
1991	42.56
1992	42.95
1993	43.18
1994	43.35
1995	43.45
1996	43.88
1997	44.19
1998	44.37
1999	44.42
2000	44.38
2001	44.76
2002	44.96
2003	45.06
2004	45.08
2005	45.04
2006	45.01
2007	44.9
2008	44.68
2009	44.28
2010	43.91
2011	43.59
2012	43.21
2013	42.78
2014	42.37
2015	41.93
2016	41.29
2017	40.66
2018	40.06
2019	39.45