| Year | Value | | 2022 | 1.430432066869 | | 2021 | 1.8942483422712 | | 2020 | 1.7398873329818 | | 2019 | 1.7521992806022 | | 2018 | 1.7346935485358 | | 2017 | 1.9769284325721 | | 2016 | 1.9793553328459 | | 2015 | 2.4170111657596 | | 2014 | 2.4126470119005 | | 2013 | 2.1540482426991 | | 2012 | 2.15519951244 | | 2011 | 2.6853186530299 | | 2010 | 2.7007478403934 | | 2009 | 3.161898710043 | | 2008 | 3.243601784026 | | 2007 | 3.2606083570292 | | 2006 | 2.7987735990309 | | 2005 | 2.6395333951407 | | 2004 | 2.9973584791957 | | 2003 | 2.8689118272584 | | 2002 | 3.3425894402144 | | 2001 | 4.2869905894923 | | 2000 | 5.033872968417 | | 1999 | 4.0301638395602 | | 1998 | 4.6434640811796 | | 1997 | 4.6306020737459 | | 1996 | 5.5197831611398 | | 1995 | 5.8611322427415 | | 1994 | 3.7293380580365 | | 1993 | 3.4317856535186 | | 1992 | 3.3676399009601 | | 1991 | 3.082087848635 | | 1990 | 2.3284874325635 | | 1989 | 1.7985954242113 | | 1988 | 2.3711832490923 | | 1987 | 3.3931467088241 | | 1986 | 2.6966580117454 | | 1985 | 3.1607698229407 | | 1984 | 0.92243050225697 | | 1983 | 0.8891374248567 | | 1982 | 0.54474092585501 | | 1981 | 0.62679842362214 | | 1980 | 0.76577930764953 | | 1979 | 0.83446274839178 | | 1978 | 0.80300011719208 | | 1977 | 0.68437388414316 | | 1976 | 0.65923914842896 | | 1975 | 0.80358956992889 | | 1974 | 0.7950864498759 | | 1973 | 0.87480982395132 | | 1971 | 1.3626334519573 | | 1970 | 0.91664227166276 | | 1969 | 0.80739632321505 | | 1968 | 0.79453205188019 | | 1967 | 0.84513666039615 | | 1966 | 0.87291591699652 | | 1965 | 0.85261009401287 | | 1964 | 0.85172590786603 | | 1963 | 0.89779192630723 | | 1962 | 1.0828550932568 | | 1961 | 1.1832727272727 | | 1960 | 1.1830523646129 |
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