| Year | Value | | 2022 | 1.4463591842758 | | 2021 | 1.6358588900273 | | 2020 | 1.7203106242392 | | 2019 | 1.6884681734386 | | 2018 | 1.7251645516038 | | 2017 | 1.7569991854466 | | 2016 | 1.7650265327558 | | 2015 | 1.7546003808327 | | 2014 | 1.7309439387877 | | 2013 | 1.6944673235245 | | 2012 | 1.6340620485791 | | 2011 | 1.5629826656329 | | 2010 | 1.5047354003649 | | 2009 | 1.4303035696071 | | 2008 | 1.3363016636181 | | 2007 | 1.2473242341721 | | 2006 | 1.1998352284496 | | 2005 | 1.2023400018231 | | 2004 | 1.2442210499652 | | 2003 | 1.4143429021858 | | 2002 | 1.7155895364023 | | 2001 | 2.0275794088281 | | 2000 | 2.2719493666929 | | 1999 | 2.4088375844172 | | 1998 | 2.4911507679185 | | 1997 | 2.5829747347243 | | 1996 | 2.746102750338 | | 1995 | 2.9663163692169 | | 1994 | 3.1691384908124 | | 1993 | 3.2408462889126 | | 1992 | 3.2025769660547 | | 1991 | 3.3476897123045 | | 1990 | 6.0943607304661 | | 1989 | 6.422109395311 | | 1988 | 3.5833762448412 | | 1987 | 3.2653716374668 | | 1986 | 3.1225694565225 | | 1985 | 2.9061491979308 | | 1984 | 2.7599743350489 | | 1983 | 2.7044650725802 | | 1982 | 1.8190950374997 | | 1981 | 1.1612710388372 | | 1980 | 1.930410097462 | | 1979 | 1.6122647464418 | | 1978 | 1.7037752112189 | | 1977 | 2.655481756571 | | 1976 | 2.8418274854227 | | 1975 | 3.0675443304544 | | 1974 | 3.0059415122122 | | 1973 | 2.991005034289 | | 1972 | 2.9940021771984 | | 1971 | 2.9422375663672 | | 1970 | 2.9028197490953 | | 1969 | 2.8305891432417 | | 1968 | 2.7556546604634 | | 1967 | 2.6677879262535 | | 1966 | 2.5409840831494 | | 1965 | 2.4360771752537 | | 1964 | 2.315506172558 | | 1963 | 2.1835174914565 | | 1962 | 2.0381999020013 | | 1961 | 1.8870907128584 |
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