Year	Percent
1991	23.67
1992	22.24
1993	19.99
1994	17.89
1995	16.11
1996	15.93
1997	15.77
1998	15.5
1999	15.05
2000	14.95
2001	14.52
2002	14.07
2003	13.97
2004	13.6
2005	13.13
2006	12.94
2007	12.6
2008	12.23
2009	11.17
2010	11.91
2011	12.96
2012	13.19
2013	13.29
2014	13.11
2015	12.36
2016	14.15
2017	13.92
2018	13.63
2019	13.41