Year	Percent
1986	77.83908
1987	76.51841
1988	77.25162
1989	78.54613
1990	79.23704
1991	79.10265
1992	78.25147
1993	78.27507
1994	78.25234
1995	78.72132
1996	78.97046
1997	79.6042
1998	80.37103
1999	81.39726
2000	82.48893
2001	82.4412
2002	83.27565
2003	83.85333
2004	83.81211
2005	83.68925
2006	83.77919
2007	83.82021
2008	83.67834
2009	84.39176
2010	84.47556
2011	84.72512
2012	83.82672
2013	83.28456
2014	83.43413
2015	83.63448
2016	83.95594
2017	84.43033