| Year | Value | | 2022 | 7.922048831479 | | 2021 | 2.5183710961421 | | 2020 | 0.98948670377249 | | 2019 | 1.7381046008651 | | 2018 | 2.2928399034594 | | 2017 | 2.5577557755775 | | 2016 | 1.0084173681141 | | 2015 | 0.36804684232536 | | 2014 | 1.4511201629328 | | 2013 | 2.2916666666666 | | 2012 | 2.5732347965453 | | 2011 | 3.8561124468282 | | 2010 | 2.4926547246707 | | 2009 | 1.9617317356011 | | 2008 | 3.5214085634254 | | 2007 | 2.3865615077333 | | 2006 | 2.4556616643929 | | 2005 | 2.0891364902507 | | 2004 | 1.3903975668042 | | 2003 | 1.3765003854201 | | 2002 | 1.5204024594745 | | 2001 | 1.5323496027242 | | 2000 | 1.1829562421041 | | 1999 | 1.7529508005142 | | 1998 | 1.8205616373156 | | 1997 | 2.2011431351088 | | 1996 | 2.8517823639775 | | 1995 | 2.6974951830443 | | 1994 | 2.2190126050421 | | 1993 | 2.558577969297 | | 1992 | 4.5915492957746 | | 1991 | 7.4617829574693 | | 1990 | 8.0634609093883 | | 1989 | 5.7602490918526 | | 1988 | 4.155351715831 | | 1987 | 4.1489223205294 | | 1986 | 3.4276094036931 | | 1985 | 6.0713943401512 | | 1984 | 4.9607109782193 | | 1983 | 4.6093032726978 | | 1982 | 8.5988638333219 | | 1981 | 11.87662651423 | | 1980 | 17.965924265686 | | 1979 | 13.421279977401 | | 1978 | 8.2631410386077 | | 1977 | 15.840266745877 | | 1976 | 16.559522558808 | | 1975 | 24.207287674329 | | 1974 | 16.044011188986 | | 1973 | 9.1960331665781 | | 1972 | 7.071098394798 | | 1971 | 9.4448374233713 | | 1970 | 6.3665684172744 | | 1969 | 5.4466636304889 | | 1968 | 4.6974279882724 | | 1967 | 2.482115604748 | | 1966 | 3.9096177921189 | | 1965 | 4.7737745538691 | | 1964 | 3.2815869469721 | | 1963 | 2.0185435597623 | | 1962 | 4.1964988823855 | | 1961 | 3.4474962304662 | | 1960 | 1.0035757039017 |
|