Year	Percent
1991	19.10888
1992	18.49306
1993	19.66862
1994	24.41357
1995	22.02083
1996	22.12944
1997	22.91824
1998	19.32491
1999	17.58807
2000	15.77301
2001	15.74672
2002	15.05573
2003	16.9783
2004	16.63348
2005	17.01694
2006	17.13968
2007	15.7741
2008	16.43718
2009	13.80421
2010	16.18704
2011	17.05457
2012	15.07711
2013	15.40886
2014	16.29175
2015	16.83478
2016	17.97811
2017	19.47372