Year	Percent
1990	27.34
1991	26.31
1992	27.16
1993	27.7
1994	25.95
1995	27.45
1996	25.33
1997	25.96
1998	24.79
1999	24.83
2000	24.68
2001	23.52
2002	23.17
2003	22.29
2004	21.64
2005	21.31
2006	20.15
2007	19.74
2008	18.93
2009	18.43
2010	18.04
2011	17.43
2012	17.57
2013	17.11
2014	16.66
2015	16.23
2016	15.82
2017	15.43
2018	15.21
2019	15.1