| Year | Value | | 2022 | 5.2223674836973 | | 2021 | 1.6423314103838 | | 2020 | 0.47649885272507 | | 2019 | 1.1082549228829 | | 2018 | 1.850815083155 | | 2017 | 1.0322827506466 | | 2016 | 0.18333486112386 | | 2015 | 0.037514380512518 | | 2014 | 0.50775882293799 | | 2013 | 0.86371549786181 | | 2012 | 1.9541953161351 | | 2011 | 2.1115979517499 | | 2010 | 1.5311227042093 | | 2009 | 0.087620478157455 | | 2008 | 2.8128619491479 | | 2007 | 1.4879980595386 | | 2006 | 1.6751244960872 | | 2005 | 1.7458693638048 | | 2004 | 2.1420896464024 | | 2003 | 2.0984721914692 | | 2002 | 1.9234122872706 | | 2001 | 1.634780795496 | | 2000 | 1.6759598872093 | | 1999 | 0.53714163913464 | | 1998 | 0.65112686783305 | | 1997 | 1.2039429402696 | | 1996 | 1.9828836508974 | | 1995 | 1.796481420956 | | 1994 | 1.6555153292699 | | 1993 | 2.1044627712464 | | 1992 | 2.3637604626935 | | 1991 | 3.2134073240969 | | 1990 | 3.1942833802947 | | 1989 | 3.4983022070075 | | 1988 | 2.7008152750811 | | 1987 | 3.2888982140013 | | 1986 | 2.5385259178142 | | 1985 | 5.8310997385452 | | 1984 | 7.6738026224732 | | 1983 | 9.4595484723532 | | 1982 | 11.978471952381 | | 1981 | 13.314405568007 | | 1980 | 13.562578848302 | | 1979 | 10.646734171666 | | 1978 | 9.2505584672443 | | 1977 | 9.4945546719043 | | 1976 | 9.6254957815553 | | 1975 | 11.685927249323 | | 1974 | 13.649317472814 | | 1973 | 7.3806010639891 | | 1972 | 6.0630030971819 | | 1971 | 5.397518655951 | | 1970 | 5.2996412456268 | | 1969 | 6.0459628417389 | | 1968 | 4.5432048640201 | | 1967 | 2.7917770943515 | | 1966 | 2.6020007663644 | | 1965 | 2.7031045587308 | | 1964 | 3.2111917029311 | | 1963 | 4.9991528979684 | | 1962 | 5.3312800706564 | | 1961 | 2.4004610454632 | | 1960 | 4.1399357551844 |
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