Year	Percent
1991	31.06
1992	30.87
1993	30.58
1994	30.24
1995	29.76
1996	29.18
1997	28.62
1998	28.22
1999	28.01
2000	27.99
2001	27.86
2002	27.85
2003	28.06
2004	28.39
2005	28.65
2006	28.41
2007	28.17
2008	28.06
2009	27.89
2010	27.84
2011	27.37
2012	26.92
2013	26.69
2014	26.69
2015	26.67
2016	26.32
2017	26.07
2018	26.05
2019	26.19