| Year | Value | | 2022 | 1.8471891564903 | | 2021 | 2.4784823269984 | | 2020 | 2.8921538416422 | | 2019 | 2.3454055352425 | | 2018 | 2.1433889563862 | | 2017 | 3.3842558856908 | | 2016 | 4.9427398187982 | | 2014 | 3.940357267487 | | 2013 | 2.0444755189805 | | 2010 | 1.6625904477394 | | 2008 | 1.7902794102278 | | 2007 | 1.9162889436872 | | 2006 | 1.5693429185719 | | 2005 | 1.5181379409281 | | 2004 | 2.4401799027708 | | 2003 | 2.4322933985532 | | 2002 | 2.1233523835068 | | 2001 | 1.7922245405252 | | 1993 | 3.6448691082442 | | 1992 | 3.8292886077865 | | 1987 | 4.3741673906748 | | 1985 | 2.5751957148743 | | 1984 | 2.2531038080334 | | 1982 | 3.3450456781448 | | 1981 | 3.1870961786967 | | 1980 | 3.3659822419534 | | 1979 | 4.3937131630648 | | 1978 | 4.3197175995966 | | 1977 | 4.9532195927353 | | 1976 | 4.7318339100346 | | 1975 | 4.4974937343358 | | 1974 | 4.2408759124088 | | 1973 | 4.2202729044834 | | 1972 | 3.5296703296703 | | 1971 | 4.6002430133657 | | 1970 | 4.8604026845638 |
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