| Year | Value | | 2022 | 7.656874561046 | | 2021 | 6.1109091637817 | | 2020 | 5.4048146718449 | | 2019 | 5.2358599942544 | | 2018 | 4.6898197612986 | | 2017 | 8.0057227913468 | | 2016 | 6.2971575245626 | | 2015 | 6.582174402504 | | 2014 | 6.8781549927594 | | 2013 | 5.7174935703774 | | 2012 | 9.3777674815511 | | 2011 | 14.022493963848 | | 2010 | 3.9613888911539 | | 2009 | 9.2341259239465 | | 2008 | 26.239816644506 | | 2007 | 9.7588802302753 | | 2006 | 14.453734208171 | | 2005 | 10.312778357468 | | 2004 | 11.624035544243 | | 2003 | 9.8156906297965 | | 2002 | 1.9613082173916 | | 2001 | 5.7385981434146 | | 2000 | 9.9800251535098 | | 1999 | 5.7420010952048 | | 1998 | 6.7224365075393 | | 1997 | 11.361845050578 | | 1996 | 8.8640874157751 | | 1995 | 1.5543281605501 | | 1994 | 28.814389430673 | | 1993 | 45.978881303622 | | 1992 | 27.332364447578 | | 1991 | 20.084495575463 | | 1990 | 17.78181442992 | | 1989 | 13.789317276388 | | 1988 | 12.264963048158 | | 1987 | 8.6376731898008 | | 1986 | 2.5342759889289 | | 1985 | 13.006566421883 | | 1984 | 10.284098213138 | | 1983 | 11.397782736852 | | 1982 | 20.666714666283 | | 1981 | 11.603053435114 | | 1980 | 13.858181456248 | | 1979 | 7.9793526184878 | | 1978 | 16.931782458284 | | 1977 | 14.820964481894 | | 1976 | 11.449030493276 | | 1975 | 19.120184013605 | | 1974 | 17.809948033182 | | 1973 | 9.281194223321 | | 1972 | 5.8316447431101 | | 1971 | 3.7802061254491 | | 1970 | 2.1885270390744 | | 1969 | 0.17150100656236 | | 1968 | 0.36671157005104 | | 1967 | 1.759195795983 | | 1966 | 5.0143953932341 | | 1965 | 3.5785288280674 | | 1964 | 0.099304866931434 | | 1963 | 0.69767441860458 | | 1962 | 3.1175059952038 | | 1961 | 2.4570024570025 | | 1960 | 1.2437810945273 |
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