Year	Percent
1987	88.35172
1988	88.09691
1989	88.09556
1990	87.90581
1991	87.17653
1992	86.77297
1993	86.17257
1994	86.29334
1995	86.0347
1996	85.47576
1997	84.5757
1998	84.41905
1999	84.55257
2000	85.17399
2001	85.81422
2002	85.85077
2003	85.64924
2004	85.57311
2005	85.41891
2006	85.69506
2007	85.4628
2008	85.35432
2009	84.85004
2010	85.06508
2011	85.38834
2012	85.45613
2013	85.39794
2014	85.46388
2015	85.37195
2016	85.69922
2017	85.45058