| Year | Value | | 2022 | 8.3087551155892 | | 2021 | 4.4442397018974 | | 2020 | 2.8479240151867 | | 2019 | 3.0139717915605 | | 2018 | 2.6829176826739 | | 2017 | 1.760415591806 | | 2016 | 1.6969276199775 | | 2015 | 1.6330555818133 | | 2014 | 2.0446148153933 | | 2013 | 3.8722792374825 | | 2012 | 5.185899887507 | | 2011 | 4.0010266434312 | | 2010 | 5.3967311316748 | | 2009 | 12.003129846174 | | 2008 | 12.694394277588 | | 2007 | 5.0515573649215 | | 2006 | 6.6870790613666 | | 2005 | 3.9870478280659 | | 2004 | 3.1581932429846 | | 2003 | 2.0556632975374 | | 2002 | 5.1970223021663 | | 2001 | 6.4050855038687 | | 2000 | 5.1364712324515 | | 1999 | 3.2318326090647 | | 1998 | 1.6592417095343 | | 1997 | 1.8154308028224 | | 1996 | 2.260418982673 | | 1995 | 1.6512315011666 | | 1994 | 1.5526562749578 | | 1993 | 4.0428529107695 | | 1992 | 3.9477117682403 | | 1991 | 6.8087788794363 | | 1990 | 15.510721994253 | | 1989 | 20.758195033449 | | 1988 | 25.725509085284 | | 1987 | 18.29776822323 | | 1986 | 22.128401187665 | | 1985 | 31.99462902407 | | 1984 | 30.852397077091 | | 1983 | 83.950046193703 | | 1982 | 50.243226389676 | | 1981 | 51.793241601011 | | 1980 | 58.528426089365 | | 1979 | 44.444455804374 | | 1978 | 43.749998285361 | | 1977 | 30.316741272593 | | 1976 | 32.035110223609 | | 1975 | 49.361338233405 | | 1974 | 42.516181958529 | | 1973 | 21.35493091683 | | 1972 | 9.8113239127997 | | 1971 | 6.7318745298099 | | 1970 | 13.372475149185 | | 1969 | 21.763294919345 | | 1968 | 15.231798403425 | | 1967 | 3.3202186782153 | | 1966 | 10.686643034239 | | 1965 | 7.3170694278335 | | 1964 | 19.245054357258 | | 1963 | 12.92802307559 | | 1962 | 11.016292445577 | | 1961 | 4.7116149967935 | | 1960 | 1.9883972390203 |
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