| Year | Value | | 2021 | 65.380367686302 | | 2020 | 66.544058826076 | | 2019 | 67.243725885179 | | 2018 | 67.041963984025 | | 2017 | 66.847703107922 | | 2016 | 66.425040202285 | | 2015 | 65.830097185259 | | 2014 | 65.17864139546 | | 2013 | 64.711251758506 | | 2012 | 64.164326258427 | | 2011 | 63.612756161279 | | 2010 | 63.159182651937 | | 2009 | 62.448091465969 | | 2008 | 61.793472310569 | | 2007 | 61.015490298285 | | 2006 | 60.23574137472 | | 2005 | 59.5534673915 | | 2004 | 59.153945226449 | | 2003 | 58.892309128216 | | 2002 | 58.638101972706 | | 2001 | 58.584940364747 | | 2000 | 58.56639148887 | | 1999 | 57.839740456666 | | 1998 | 58.1103756244 | | 1997 | 58.484653173136 | | 1996 | 58.847383794909 | | 1995 | 58.860579262501 | | 1994 | 59.081961943674 | | 1993 | 59.366862037625 | | 1992 | 59.349617944749 | | 1991 | 59.492232480147 | | 1990 | 59.557018604447 | | 1989 | 59.615381983504 | | 1988 | 58.747486288649 | | 1987 | 58.588367203506 | | 1986 | 58.173055100806 | | 1985 | 57.774121670563 | | 1984 | 57.409411654974 | | 1983 | 56.926212066213 | | 1982 | 56.595463024195 | | 1981 | 56.079946840377 | | 1980 | 55.70785774776 | | 1979 | 55.16842928989 | | 1978 | 54.762700772561 | | 1977 | 54.612329863466 | | 1976 | 53.998846463136 | | 1975 | 53.770593587669 | | 1974 | 53.119254941549 | | 1973 | 53.9803137994 | | 1972 | 53.535050213835 | | 1971 | 52.904839263487 | | 1970 | 52.351419429266 | | 1969 | 51.930553089067 | | 1968 | 52.125766072119 | | 1967 | 51.838475821974 | | 1966 | 51.562266529853 | | 1965 | 51.244909448867 | | 1964 | 50.589052477242 | | 1963 | 50.02077794367 | | 1962 | 50.17582484052 | | 1961 | 49.780892156704 | | 1960 | 49.32760542187 |
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