Year	Percent
1991	33.28
1992	30.73
1993	29.31
1994	27.14
1995	26.18
1996	25.43
1997	25.11
1998	25.37
1999	25.44
2000	26
2001	26.26
2002	25.73
2003	25.25
2004	27.81
2005	25.73
2006	25.36
2007	24.78
2008	24.53
2009	21.77
2010	20.4
2011	19.24
2012	18.41
2013	16.15
2014	15.47
2015	15.6
2016	16.6
2017	17.14
2018	17.72
2019	18.43