Year	Percent
1986	80.85706
1987	80.88539
1988	80.9488
1989	80.55002
1990	80.68468
1991	79.45387
1992	78.81603
1993	79.27745
1994	77.81472
1995	76.54911
1996	75.92053
1997	77.45155
1998	76.69097
1999	77.9731
2000	78.39046
2001	77.55465
2002	77.43166
2003	78.38722
2004	78.65836
2005	79.25548
2006	80.63699
2007	80.15294
2008	80.7794
2009	80.6278
2010	81.40686
2011	81.70717
2012	81.63879
2013	81.34608
2014	82.10261
2015	82.97532
2016	83.05899
2017	83.5223