Year	Percent
1997	87.91939
1998	86.63786
1999	85.585
2000	85.0909
2001	84.83818
2002	84.11971
2003	82.71286
2004	83.1912
2005	84.13078
2006	83.97789
2007	83.95676
2008	84.04001
2009	83.3423
2010	82.548
2011	82.2881
2012	81.85739
2013	82.33878
2014	82.24513
2015	82.90247
2016	83.13357
2017	83.21831