Year	%
1971	99.9498
1972	99.48106
1973	99.75724
1974	99.74464
1975	100
1976	99.82437
1977	100
1978	99.95626
1979	99.86301
1980	99.92948
1981	99.92842
1982	99.92933
1983	100
1984	99.93065
1985	100
1991	100
1992	100
1993	99.51642
1994	98.10594
1995	98.53667
1996	99.712
1998	98.71108
1999	99.85135
2000	99.88538
2001	99.55014
2002	99.89862
2003	98.76936
2004	99.57495
2005	99.66062
2006	99.93828
2007	98.70138
2008	99.07343
2009	98.55389
2010	98.44346
2011	98.49313
2012	98.10813
2013	98.31024
2014	98.38697
2015	98.07925
2016	98.01376
2017	98.15973