Year	Percent
1980	90.33647
1981	89.27395
1982	91.59292
1983	80.64657
1984	80.38582
1989	72.86929
1990	86.61615
1991	83.72146
1992	79.4695
1993	85.5881
1994	85.63162
1995	84.73017
1997	88.04523
1998	88.41627
1999	89.51998
2000	89.61765
2001	90.55755
2002	91.32979
2003	89.33895
2004	88.74375
2005	91.55983
2006	90.84721
2007	86.5777
2008	89.9085
2009	90.04498
2010	87.72274
2011	90.10275
2012	87.54122
2013	87.96392
2015	83.45237
2016	82.14008
2017	79.806