Year	Percent
1991	29.43
1992	28.95
1993	28.42
1994	28.03
1995	27.69
1996	27.38
1997	27.19
1998	26.99
1999	26.73
2000	26.53
2001	26.42
2002	26.23
2003	26.08
2004	26.02
2005	26
2006	26.8
2007	27.64
2008	28.32
2009	28.5
2010	30.07
2011	31.94
2012	33.63
2013	33.65
2014	33.67
2015	33.66
2016	33.6
2017	33.5
2018	33.3
2019	33.02