| Year | Value | | 2024 | 1.3658054079804 | | 2023 | 8.4780517442154 | | 2022 | -1.6106803048669 | | 2021 | 1.2303954131838 | | 2020 | 0.84593714735704 | | 2019 | 0.70672860131431 | | 2018 | 1.0638975418302 | | 2017 | 0.66563189313511 | | 2016 | 0.18814970444814 | | 2015 | 0.90042496329157 | | 2014 | 1.8951418189878 | | 2013 | 2.1848861853069 | | 2012 | 3.0148995033499 | | 2011 | 3.8087905813963 | | 2010 | 3.2475884244372 | | 2009 | 0.84571609231672 | | 2008 | 5.4684894964985 | | 2007 | 2.241540952868 | | 2006 | 4.6374743601176 | | 2005 | 4.5403691963453 | | 2004 | 2.7591492623108 | | 2003 | 1.8043499463572 | | 2002 | 0.69730897662545 | | 2001 | 1.6269088731409 | | 2000 | 1.5919691746097 | | 1999 | 0.28472645922303 | | 1998 | 7.9947287502746 | | 1997 | 5.625797471291 | | 1996 | 5.8051055473735 | | 1995 | 5.8181818181819 | | 1994 | 5.0477489768075 | | 1993 | 3.3121916842847 | | 1992 | 4.1391457507706 | | 1991 | 5.709852598914 | | 1990 | 5.8639947437583 | | 1989 | 5.3554650798622 | | 1988 | 3.8627307473365 | | 1987 | 2.4664611282395 | | 1986 | 1.8416759680605 | | 1985 | 2.4317312343347 | | 1984 | 0.86489843027932 | | 1983 | 3.7265366212407 | | 1982 | 5.2590799031683 | | 1981 | 12.662993071021 | | 1980 | 19.703500522778 | | 1979 | 9.8973659655992 | | 1978 | 7.9240898530379 | | 1977 | 7.6012668776903 | | 1976 | 4.1493055549479 | | 1975 | 5.3300970874987 |
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