| Year | Value | | 2015 | 1.774998670992 | | 2014 | 0.9443538046339 | | 2013 | 4.9080896043943 | | 2012 | -8.6537179435339 | | 2011 | -14.54194579914 | | 2010 | -19.862022423821 | | 2009 | -30.459883478761 | | 2008 | -38.714955663836 | | 2007 | -36.994219945343 | | 2006 | -45.861162799417 | | 2005 | -65.694055928517 | | 2004 | -60.071115668718 | | 2003 | -41.720959160029 | | 2002 | -50.41935193786 | | 2001 | -41.313700490392 | | 2000 | -48.844189589949 | | 1999 | -24.04789959301 | | 1998 | -1.8920438168564 | | 1997 | 0.46478743249714 | | 1996 | 19.505388675091 | | 1995 | 19.610423863588 | | 1994 | 22.872906566381 | | 1993 | 26.566739392922 | | 1992 | 29.871003856545 | | 1991 | 38.0963022679 | | 1990 | 41.933965163383 | | 1989 | 45.605606832597 | | 1988 | 55.531930712426 | | 1987 | 58.354363282844 | | 1986 | 66.76010481158 | | 1985 | 74.203271810946 | | 1984 | 79.382054760765 | | 1983 | 81.25831816834 | | 1982 | 85.286990672715 | | 1981 | 90.976836010084 | | 1980 | 95.023042298285 | | 1979 | 95.27438064686 | | 1978 | 95.588197048402 | | 1977 | 95.317759250226 | | 1976 | 96.862048823662 | | 1975 | 96.987309154276 | | 1974 | 97.458676398596 | | 1973 | 97.756043914267 | | 1972 | 97.745924269074 | | 1971 | 98.220932879205 | | 1970 | 98.070334052187 | | 1969 | 98.967873337796 | | 1968 | 97.891668612873 | | 1967 | 96.362860892078 | | 1966 | 94.973531526364 | | 1965 | 94.158304629443 | | 1964 | 93.440536472879 | | 1963 | 92.291223771041 | | 1962 | 91.389255796683 | | 1961 | 90.008278975208 | | 1960 | 88.701391342897 |
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