Year	Percent
1983	87.85502
1984	86.65531
1985	86.43125
1986	86.2432
1987	84.66731
1988	84.28161
1989	82.29418
1990	82.18951
1991	82.58977
1992	83.215
1993	83.25412
1994	82.70448
1995	82.62355
1996	83.26087
1997	83.65818
1998	84.33581
1999	83.80199
2000	84.56416
2001	84.29874
2002	84.11683
2003	83.55201
2004	82.99409
2005	83.16546
2006	82.94682
2007	82.75485
2008	82.50566
2009	82.40559
2010	82.07103
2011	81.9935
2012	81.13684
2013	81.1999
2014	80.92444
2015	81.27621
2016	80.90636
2017	81.1805