Year	Percent
1976	91.49899
1977	91.39597
1978	91.33573
1979	91.16367
1980	90.89524
1981	90.94649
1982	90.64911
1983	90.40919
1984	90.65629
1985	90.85536
1986	90.91143
1987	90.83003
1988	90.78151
1989	90.9388
1990	90.97637
1991	90.69507
1992	90.86236
1993	90.54413
1994	91.24202
1995	91.5363
1996	91.61867
1997	91.7507
1998	91.91371
1999	92.18999
2000	92.06464
2001	92.14789
2002	92.25685
2003	91.87381
2004	91.83052
2005	91.883
2006	91.96574
2007	92.15571
2008	92.31494
2009	92.22177
2010	92.23804
2011	92.65142
2012	92.77082
2013	93.06113
2014	93.1297
2015	93.08509
2016	93.09589
2017	93.3893