| Year | Value | | 2022 | 10.177231354617 | | 2021 | 3.4950575739945 | | 2020 | 2.5266350008471 | | 2019 | 3.5230193274145 | | 2018 | 3.2405693293057 | | 2017 | 4.3143132569501 | | 2016 | 7.5134602462768 | | 2015 | 4.9898311584953 | | 2014 | 2.8988378776174 | | 2013 | 2.0169922431038 | | 2012 | 3.1693018884005 | | 2011 | 3.4150334477625 | | 2010 | 2.2720022789201 | | 2009 | 4.2025166121648 | | 2008 | 6.9968849555451 | | 2007 | 5.5443848581516 | | 2006 | 4.2934236362893 | | 2005 | 5.051019626897 | | 2004 | 5.904020055465 | | 2003 | 7.1297886294186 | | 2002 | 6.3515072877887 | | 2001 | 7.9655609030483 | | 2000 | 9.2253481858537 | | 1999 | 10.873687085747 | | 1998 | 18.676979927667 | | 1997 | 18.470021711909 | | 1996 | 20.79757551274 | | 1995 | 20.891793019485 | | 1994 | 22.846241755305 | | 1993 | 22.442482853328 | | 1992 | 27.010626623136 | | 1991 | 30.387820485444 | | 1990 | 29.152024597622 | | 1989 | 25.867548083199 | | 1988 | 28.10839697717 | | 1987 | 23.302028364018 | | 1986 | 18.842463161241 | | 1985 | 24.090174368125 | | 1984 | 16.161617136143 | | 1983 | 19.597317062476 | | 1982 | 24.720988252859 | | 1981 | 27.453762434799 | | 1980 | 26.552653149536 | | 1979 | 24.134075744046 | | 1978 | 17.763159085346 | | 1977 | 33.802818357982 | | 1976 | 19.831224916793 | | 1975 | 23.437502565055 | | 1974 | 23.87095736567 | | 1973 | 22.529648678184 | | 1972 | 12.444458990773 | | 1971 | 11.940261697922 | | 1970 | 6.9086227584824 | | 1969 | 6.9816630795538 | | 1968 | 7.4475387831777 | | 1967 | 8.3281913642595 | | 1966 | 16.72816827486 | | 1965 | 7.5906836693158 | | 1964 | 17.072435216455 | | 1963 | 26.355435525047 | | 1962 | 4.6970939506247 | | 1961 | 8.2831904564872 | | 1960 | 5.8140762820499 |
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