Year	Percent
1991	20.82
1992	19.87
1993	23.63
1994	24.29
1995	24.17
1996	24.93
1997	26.97
1998	27.8
1999	28.46
2000	27.84
2001	26.62
2002	25.51
2003	24.76
2004	24.63
2005	23.21
2006	22.99
2007	22.49
2008	21.19
2009	18.98
2010	17.99
2011	17.72
2012	17.79
2013	17.42
2014	17.06
2015	17.25
2016	16.82
2017	16.57
2018	16.34
2019	15.79