Year	Percent
1991	20.03
1992	20.53
1993	21.54
1994	22.05
1995	22.83
1996	22.18
1997	21.99
1998	21.73
1999	21.59
2000	22.66
2001	21.98
2002	21.59
2003	20.32
2004	19.35
2005	19.19
2006	19.08
2007	19.43
2008	19.87
2009	18.62
2010	18.09
2011	19.11
2012	17.74
2013	18.23
2014	17.36
2015	19.3
2016	17.33
2017	17.12
2018	17.41
2019	16.47