| Year | Value | | 2022 | 0.58187583285324 | | 2021 | 0.59715159452762 | | 2020 | 0.59205394258279 | | 2019 | 0.53444340051175 | | 2018 | 0.55487296594627 | | 2017 | 0.6109561448905 | | 2016 | 0.69028832865205 | | 2015 | 0.78693541938077 | | 2014 | 0.83158924761648 | | 2013 | 0.93432629329517 | | 2012 | 1.0837075607137 | | 2011 | 1.1993833749614 | | 2010 | 1.3640660545341 | | 2009 | 1.5293679498773 | | 2008 | 1.4945790618761 | | 2007 | 1.376233272436 | | 2006 | 1.2764224951944 | | 2005 | 1.1687054501892 | | 2004 | 1.1030834834321 | | 2003 | 1.1335215075252 | | 2002 | 1.2776394380085 | | 2001 | 1.5337115601666 | | 2000 | 1.6577934137667 | | 1999 | 1.7064071466556 | | 1998 | 1.883357705203 | | 1997 | 2.0140239393202 | | 1996 | 2.0261771627752 | | 1995 | 1.957691517641 | | 1994 | 1.863024705445 | | 1993 | 1.8009115538285 | | 1992 | 1.5979387967708 | | 1991 | 0.4820349277923 | | 1990 | 0.4851778522838 | | 1989 | 0.542244585848 | | 1988 | 0.57817592006018 | | 1987 | 0.55631027135765 | | 1986 | 0.51788031898849 | | 1985 | 0.48155909332499 | | 1984 | 0.07035253023982 | | 1983 | 0.2709759081227 | | 1982 | 0.23789984130338 | | 1981 | 0.28776998276152 | | 1980 | 0.43243978492782 | | 1979 | 0.43431795148271 | | 1978 | 0.3301001082271 | | 1977 | 0.19827182215634 | | 1976 | 0.070298772666623 | | 1975 | 0.28537363522584 | | 1974 | 0.38078705642496 | | 1973 | 0.35925029733729 | | 1972 | 0.11431750611586 | | 1971 | 0.38983388632628 | | 1970 | 1.2085068997908 | | 1969 | 1.7152319242437 | | 1968 | 1.6753560233845 | | 1967 | 1.6395419293075 | | 1966 | 1.6148830469886 | | 1965 | 1.6567305937163 | | 1964 | 1.5218170405795 | | 1963 | 1.3416471522223 | | 1962 | 1.3474460618691 | | 1961 | 1.6185034314982 |
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