Year	Percent
1991	30.96
1992	30.37
1993	28.8
1994	28.34
1995	28.53
1996	27.58
1997	26.59
1998	29.7
1999	28.73
2000	28.97
2001	27.07
2002	27.72
2003	26.75
2004	28.47
2005	25.58
2006	25.22
2007	25.08
2008	24.41
2009	23.62
2010	20.9
2011	16.97
2012	13.6
2013	12.44
2014	13.45
2015	13.25
2016	13.1
2017	14.38
2018	14.62
2019	15.19