| Year | Value | | 2022 | 4.8737806055168 | | 2021 | 1.6929953602286 | | 2020 | 1.7521515668134 | | 2019 | 1.6915376947092 | | 2018 | 1.6523680322762 | | 2017 | 1.9874228737039 | | 2016 | 1.8463975575009 | | 2015 | 2.0437947662002 | | 2014 | 1.9514268591161 | | 2013 | 1.9577567981769 | | 2012 | 1.5893849900421 | | 2011 | 1.4291639856271 | | 2010 | 1.8482080682451 | | 2009 | 2.1265899927187 | | 2008 | 2.06975934286 | | 2007 | 2.1023759768496 | | 2006 | 2.0795963879135 | | 2005 | 2.2498737786506 | | 2004 | 2.4182300752145 | | 2003 | 2.5972237770687 | | 2002 | 2.6277275481489 | | 2001 | 2.6372881922928 | | 2000 | 2.6934625467921 | | 1999 | 2.9281047987652 | | 1998 | 2.1992962898189 | | 1997 | 2.161854476166 | | 1996 | 1.9209142748233 | | 1995 | 2.2797739176786 | | 1994 | 3.1131671604737 | | 1993 | 2.7823094492496 | | 1992 | 2.6037656383316 | | 1991 | 3.6734519365214 | | 1986 | 3.8576954905501 | | 1985 | 3.4800547370803 | | 1984 | 3.9479899971422 | | 1983 | 3.8201261638811 | | 1982 | 3.3668936003618 | | 1981 | 4.1161603187928 | | 1980 | 4.1409618146489 | | 1979 | 4.5292366473386 | | 1978 | 5.0092881798381 | | 1977 | 5.3232632625697 | | 1976 | 5.4362973484713 | | 1975 | 6.1901344248378 | | 1974 | 4.8973069948044 | | 1973 | 4.904171308827 | | 1972 | 4.7777393125047 | | 1971 | 4.3659232014723 | | 1970 | 4.6111471709301 | | 1969 | 6.1198928618505 | | 1968 | 5.4275171340323 | | 1967 | 3.9069458841442 | | 1966 | 2.4692721119398 | | 1965 | 2.7147762518765 | | 1964 | 3.2393562077413 | | 1963 | 2.7967851635096 | | 1962 | 3.1904816255473 | | 1961 | 2.4397709810568 | | 1960 | 3.1298328715868 |
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