Year	Percent
1983	91.37681
1984	91.36691
1985	91.56028
1986	91.92201
1987	91.4094
1988	91.88267
1989	92.14624
1990	92.06874
1991	91.89017
1992	91.74282
1993	91.05547
1994	91.29718
1995	91.28782
1996	91.81327
1997	92.25216
1998	92.36478
1999	92.21126
2000	92.26687
2001	93.65803
2002	93.40527
2003	93.78937
2004	93.13225
2005	93.16857
2006	93.44497
2007	93.99586
2008	94.66152
2009	92.25222
2010	92.48951
2011	92.21608
2012	92.03008
2013	91.87242
2014	92.07209
2015	90.48979
2016	90.29215
2017	90.52873