| Year | Value | | 2022 | 0.42097447455256 | | 2021 | 0.84257600312602 | | 2020 | 1.6731008261205 | | 2019 | 1.7284650283834 | | 2018 | 0.78803388077999 | | 2017 | 1.5023313732953 | | 2016 | 2.9039784611434 | | 2015 | 2.9802231739317 | | 2014 | 2.9022658344768 | | 2013 | 5.5230395256431 | | 2012 | 3.5405828188292 | | 2011 | -1.8402973019909 | | 2010 | 0.53299098267355 | | 2009 | 0.80349982154697 | | 2008 | 0.45149468065039 | | 2007 | 1.1003501255017 | | 2006 | 1.2941852818996 | | 2005 | 1.5970048872604 | | 2004 | 3.1772528737293 | | 2003 | 2.2330603873018 | | 2002 | 0.57676488153504 | | 2001 | 0.26505684786142 | | 2000 | -1.8343776867275 | | 1999 | 0.50061076244894 | | 1998 | 0.14414994087354 | | 1997 | 0.68684879878055 | | 1996 | 0.59042167516174 | | 1995 | 0.43896424562607 | | 1994 | 0.27691260339352 | | 1993 | 1.5134534066437 | | 1992 | 4.9875455389339 | | 1991 | 6.852589229496 | | 1990 | 7.0404739108629 | | 1989 | 7.2419888142369 | | 1988 | 7.499107013137 | | 1987 | 7.8559102352689 | | 1986 | 8.2476877510133 | | 1985 | 8.7087677920538 | | 1984 | 9.2698279606259 | | 1983 | 9.9538356287257 | | 1982 | 9.3273138213606 | | 1981 | 7.0249942677003 | | 1980 | 5.8961788803004 | | 1979 | 6.1827476302306 | | 1978 | 6.4526232426595 | | 1977 | 6.5928922347964 | | 1976 | 6.6984718312398 | | 1975 | 6.9024953102585 | | 1974 | 7.0007410431671 | | 1973 | 7.0007210639807 | | 1972 | 7.0219355785423 | | 1971 | 7.3286091828018 | | 1970 | 7.7184708320292 | | 1969 | 7.9151531693554 | | 1968 | 8.2504957043562 | | 1967 | 8.4396322369598 | | 1966 | 8.5187235684197 | | 1965 | 8.7863808109081 | | 1964 | 9.0572013062421 | | 1963 | 9.3272613273092 | | 1962 | 9.348277452563 | | 1961 | 8.7515155337816 |
|