Year	Percent
1990	24.99
1991	24.63
1992	23.86
1993	23.84
1994	24.14
1995	23.78
1996	23.55
1997	23
1998	21.52
1999	20.06
2000	18.64
2001	17.3
2002	16.01
2003	14.78
2004	13.61
2005	12.52
2006	11.52
2007	10.59
2008	10.4
2009	10.21
2010	10.03
2011	9.92
2012	9.81
2013	10.04
2014	10.29
2015	11.48
2016	12.76
2017	13.59
2018	14.07
2019	13.68