Year	Percent
1990	27.89161
1991	27.16192
1992	26.74968
1993	26.15607
1994	26.678
1995	24.88879
1996	24.993
1997	24.13059
1998	23.17582
1999	22.10978
2000	22.53696
2001	21.40656
2002	21.09321
2003	20.25731
2004	19.50284
2005	19.72517
2006	19.74464
2007	19.3011
2008	19.00886
2009	18.00579
2010	17.99412
2011	18.05063
2012	17.92247
2013	18.15402
2014	17.82977
2015	17.84822
2016	17.98518
2017	18.57391