Year	Percent
1991	41.38
1992	41.36
1993	41.27
1994	41.19
1995	41.03
1996	40.6
1997	40.11
1998	39.49
1999	38.84
2000	38.33
2001	38.06
2002	37.73
2003	37.45
2004	37.17
2005	36.82
2006	36.65
2007	36.46
2008	36.88
2009	36.92
2010	37.18
2011	37.59
2012	37.97
2013	38.36
2014	38.87
2015	39.32
2016	39.92
2017	40.25
2018	40.55
2019	40.78
2020	38.96