| Year | Value | | 2022 | 2.2107951167597 | | 2021 | 2.1136372255898 | | 2020 | 2.5340939316943 | | 2019 | 2.2233610712516 | | 2018 | 1.9430586234461 | | 2017 | 1.8698608952239 | | 2016 | 1.7451754223759 | | 2015 | 0.42834036184366 | | 2014 | 0.076949023092681 | | 2013 | 0.60824767656122 | | 2012 | 0.86865512887218 | | 2011 | 1.532276958569 | | 2010 | 2.071208345015 | | 2009 | 2.1548540970223 | | 2008 | 2.0732632800489 | | 2007 | 1.8735897550277 | | 2006 | 2.0115021231522 | | 2005 | 2.2513280302748 | | 2004 | 2.1690171807833 | | 2003 | 2.4177899818124 | | 2002 | 2.2089734281734 | | 2001 | 2.2516375150241 | | 2000 | 2.8003604789814 | | 1999 | 2.782151765735 | | 1998 | 2.7546192875739 | | 1997 | 2.7823963108865 | | 1996 | 2.6164260433397 | | 1995 | 2.7493823258035 | | 1994 | 3.1450148923656 | | 1993 | 3.2043864672605 | | 1992 | 3.1812025487041 | | 1991 | 3.1131566434123 | | 1990 | 3.0765818541647 | | 1989 | 2.4855293689038 | | 1988 | 1.5794885708332 | | 1987 | 1.2295448908003 | | 1986 | 1.1897258834479 | | 1985 | 1.1636629895768 | | 1984 | 1.1334278932095 | | 1983 | 1.1067404128178 | | 1982 | 1.0848313990975 | | 1981 | 1.0598321795412 | | 1980 | 1.0382552915364 | | 1979 | 1.0248422115858 | | 1978 | 1.0156830988825 | | 1977 | 1.0170465855943 | | 1976 | 1.4958964600834 | | 1975 | 1.9730779945106 | | 1974 | 1.9571287628841 | | 1973 | 1.9447365383722 | | 1972 | 1.9879022769448 | | 1971 | 2.0997377929629 | | 1970 | 2.242128713945 | | 1969 | 2.3150692546052 | | 1968 | 2.2732499042464 | | 1967 | 2.1996250887676 | | 1966 | 2.1232335987811 | | 1965 | 2.047511136393 | | 1964 | 1.9778186381279 | | 1963 | 1.9162121378408 | | 1962 | 1.8615798069068 | | 1961 | 1.8074337813727 |
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