Year	Percent
1991	32.55
1992	33.4
1993	33.3
1994	32.93
1995	32.12
1996	31.49
1997	30.04
1998	29.7
1999	31.08
2000	31.17
2001	29.97
2002	28.15
2003	26.27
2004	22.45
2005	19.97
2006	19.23
2007	18.66
2008	21.06
2009	16.87
2010	15.42
2011	14.03
2012	14.35
2013	14.62
2014	15.1
2015	16.58
2016	19.39
2017	20.32
2018	20.51
2019	21.03