| Year | Value | | 2022 | 2.1740912420478 | | 2021 | 2.2417673711265 | | 2020 | 2.2990303401086 | | 2019 | 2.3328406249281 | | 2018 | 2.3647130666403 | | 2017 | 2.4211348577947 | | 2016 | 2.4195089151865 | | 2015 | 2.4086871612088 | | 2014 | 2.49317673034 | | 2013 | 2.5634543181835 | | 2012 | 2.629841403865 | | 2011 | 2.6928730024304 | | 2010 | 2.7860730527666 | | 2009 | 2.7365658318246 | | 2008 | 2.5221072503598 | | 2007 | 2.2026542698717 | | 2006 | 2.2003639292847 | | 2005 | 2.6748408801911 | | 2004 | 3.3523544312401 | | 2003 | 4.0191015587932 | | 2002 | 5.6634335205726 | | 2001 | 5.785413309402 | | 2000 | 2.4047841924957 | | 1999 | 0.56402752516746 | | 1998 | 1.0151862403732 | | 1997 | 1.3175551224556 | | 1996 | 0.53557065388693 | | 1995 | 0.21289257779967 | | 1994 | 0.44744705772663 | | 1993 | 0.13671807839671 | | 1992 | -1.7651458010659 | | 1991 | 1.2128753114333 | | 1990 | 3.918799523644 | | 1989 | 2.5063579332713 | | 1988 | 2.7075346315846 | | 1987 | 2.6943212818363 | | 1986 | 2.4630818993773 | | 1985 | 2.2428280242194 | | 1984 | 2.2198542953027 | | 1983 | 2.1586835074333 | | 1982 | 2.0756816249611 | | 1981 | 2.0466620839932 | | 1980 | 2.0231633891365 | | 1979 | 1.9850688591128 | | 1978 | 1.9657699511086 | | 1977 | 1.8880895796394 | | 1976 | 1.8463497481001 | | 1975 | 1.885283640258 | | 1974 | 1.9023743531721 | | 1973 | 1.9108915246124 | | 1972 | 1.8972304503412 | | 1971 | 1.9189856138068 | | 1970 | 1.9499631013585 | | 1969 | 1.9466378038234 | | 1968 | 1.964026775187 | | 1967 | 1.9522281494637 | | 1966 | 1.9315723061841 | | 1965 | 1.9182437645623 | | 1964 | 1.8752095577613 | | 1963 | 1.8228805108307 | | 1962 | 1.771815446658 | | 1961 | 1.7127428023521 |
|