| Year | Value | | 2022 | 8.4711764559091 | | 2021 | 2.4865043812083 | | 2020 | 0.18693813970213 | | 2019 | 1.4412396694234 | | 2018 | 1.6892396580413 | | 2017 | 1.3750364152534 | | 2016 | 0.16600988437562 | | 2015 | 0.085207229696375 | | 2014 | 0.22019562819875 | | 2013 | 1.3102335561867 | | 2012 | 2.5415447410801 | | 2011 | 3.288014272198 | | 2010 | 1.5205755786839 | | 2009 | 0.4371754127927 | | 2008 | 4.1140702203382 | | 2007 | 2.4823154668954 | | 2006 | 2.7200475052927 | | 2005 | 2.5239289874716 | | 2004 | 2.2162078892627 | | 2003 | 2.0952352907229 | | 2002 | 2.3269068361586 | | 2001 | 2.8573289351883 | | 2000 | 2.9475655997748 | | 1999 | 1.8991144190705 | | 1998 | 2.3064793403599 | | 1997 | 2.223054305268 | | 1996 | 3.0239510949553 | | 1995 | 4.0864600455494 | | 1994 | 4.4142555634662 | | 1993 | 4.5979032100656 | | 1992 | 5.2705899859293 | | 1991 | 4.1786227479847 | | 1990 | 3.9751834042882 | | 1989 | 3.9272616065188 | | 1988 | 3.065040795222 | | 1987 | 3.2241529272678 | | 1986 | 2.7360525611187 | | 1985 | 5.1956219542944 | | 1984 | 7.0676563832817 | | 1983 | 8.6692715980852 | | 1982 | 9.5849276467744 | | 1981 | 11.509755837712 | | 1980 | 13.54006971278 | | 1979 | 8.4653349041488 | | 1978 | 7.5737122394973 | | 1977 | 9.7674647360704 | | 1976 | 9.7114211093591 | | 1975 | 12.227062920687 | | 1974 | 14.664845435677 | | 1973 | 7.915546149656 | | 1972 | 5.906253517241 | | 1971 | 5.0163194330344 | | 1970 | 4.1406484002703 | | 1969 | 2.6480857111123 | | 1968 | 3.2428288767945 | | 1967 | 2.9875460669517 | | 1966 | 3.4323700636613 | | 1965 | 3.6664828026259 | | 1964 | 3.656731015797 | | 1963 | 2.9216411190019 | | 1962 | 2.7526671886691 | | 1961 | 1.8708496140633 | | 1960 | 1.7411808474692 |
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