Year	Percent
1980	98.58514
1981	94.40516
1982	91.82266
1983	93.31423
1984	90.82079
1989	74.44153
1990	79.05212
1991	82.16881
1992	75.74968
1993	75.13715
1994	75.3231
1995	75.13477
1997	76.87584
1998	75.43727
1999	76.69553
2000	76.50854
2001	76.01247
2002	75.21403
2003	74.68227
2004	74.90987
2005	77.48304
2006	78.64406
2007	76.12573
2008	78.08212
2009	78.32395
2010	78.28247
2011	77.44404
2012	77.38843
2013	76.68509
2015	76.02896
2016	77.89571
2017	77.64157