Year	Percent
1983	89.79803
1984	90.70532
1985	91.26857
1986	91.67905
1987	91.82991
1988	92.44761
1989	91.95083
1990	91.71449
1991	92.05921
1992	92.13327
1993	91.89913
1994	92.41084
1995	92.2764
1996	92.29228
1997	92.18399
1998	92.12523
1999	92.0148
2000	92.60269
2001	92.82501
2002	92.5778
2003	92.38497
2004	92.71095
2005	92.44189
2006	92.17739
2007	92.194
2008	92.22674
2009	91.67408
2010	91.84432
2011	91.91033
2012	91.95941
2013	92.06559
2014	92.05355
2015	92.09797
2016	91.81524
2017	92.44554