Year	Percent
1991	39.19
1992	39.35
1993	39.28
1994	39.21
1995	39.3
1996	39.39
1997	39.38
1998	39.49
1999	39.8
2000	39.94
2001	39.55
2002	38.77
2003	38.39
2004	38.03
2005	37.76
2006	36.9
2007	35.89
2008	35.21
2009	35.04
2010	34.96
2011	34.26
2012	33.19
2013	31.94
2014	30.83
2015	29.55
2016	28.31
2017	27.43
2018	27.66
2019	29.94