Year	Percent
1980	99.61555
1981	95.08882
1982	91.8532
1983	95.86762
1984	92.78967
1989	74.78016
1990	77.31533
1991	81.81959
1992	74.98607
1993	73.06612
1994	73.26893
1995	73.20558
1997	74.67111
1998	72.76905
1999	73.90014
2000	73.96566
2001	72.95804
2002	71.56005
2003	71.75854
2004	72.30609
2005	74.98768
2006	76.3792
2007	74.00952
2008	75.86341
2009	76.19849
2010	76.53321
2011	75.05757
2012	75.31928
2013	74.50773
2015	74.55691
2016	76.99388
2017	77.18884