Year	Percent
1997	84.58409
1998	83.13798
1999	81.77218
2000	81.10905
2001	80.95206
2002	79.78284
2003	78.2222
2004	78.58528
2005	79.82208
2006	79.93452
2007	79.72673
2008	79.90939
2009	79.2956
2010	78.45674
2011	78.42612
2012	78.12359
2013	79.02332
2014	78.25909
2015	79.39035
2016	80.1315
2017	79.95029