Year	Percent
1991	39.85
1992	39.76
1993	39.58
1994	39.44
1995	39.34
1996	39.2
1997	39.09
1998	39.01
1999	38.87
2000	38.82
2001	38.3
2002	36.8
2003	37.31
2004	38.88
2005	39.1
2006	39.56
2007	40.65
2008	43.1
2009	41.25
2010	39.53
2011	39.59
2012	39.93
2013	40.53
2014	40.6
2015	41.45
2016	40.79
2017	40.99
2018	40.93
2019	40.12
2020	36.69