Year	Percent
1990	23.6
1991	18.34
1992	14.85
1993	18.19
1994	17
1995	17.92
1996	15.68
1997	16.64
1998	17.75
1999	18.57
2000	17.25
2001	17.5
2002	17.76
2003	18.01
2004	18.25
2005	18.5
2006	18.79
2007	19.06
2008	19.33
2009	19.6
2010	19.87
2011	19.81
2012	20.59
2013	21.76
2014	20.46
2015	21.86
2016	23.06
2017	23.87
2018	21.78
2019	22.28