Year	Percent
1986	76.93291
1987	75.09936
1988	76.32463
1989	78.34378
1990	79.6888
1991	79.63018
1992	79.1548
1993	79.62336
1994	80.61674
1995	80.74522
1996	81.36041
1997	82.23709
1998	82.95445
1999	84.52648
2000	85.63542
2001	85.5162
2002	86.55535
2003	87.27874
2004	87.37097
2005	87.00781
2006	87.54864
2007	87.71683
2008	87.73539
2009	88.28803
2010	88.56614
2011	88.70156
2012	88.12839
2013	87.65894
2014	87.69704
2015	87.82415
2016	87.91785
2017	88.49099