| Year | Value | | 2022 | 1.9095103105995 | | 2021 | 1.9427612825276 | | 2020 | 2.0097001107967 | | 2019 | 1.9784569484426 | | 2018 | 2.0327340045028 | | 2017 | 2.1757084269036 | | 2016 | 2.2021455619855 | | 2015 | 2.2003221195289 | | 2014 | 2.2941780158286 | | 2013 | 2.4099313640374 | | 2012 | 2.5259564430229 | | 2011 | 2.6554350581204 | | 2010 | 2.8175240671163 | | 2009 | 2.9606918765214 | | 2008 | 2.9788451547923 | | 2007 | 2.9658248009106 | | 2006 | 2.9747111165204 | | 2005 | 2.9765807398306 | | 2004 | 2.989515436241 | | 2003 | 2.9674433527342 | | 2002 | 3.0336097775699 | | 2001 | 3.0288268548235 | | 2000 | 2.9154468419839 | | 1999 | 2.801269321539 | | 1998 | 2.6891602736603 | | 1997 | 2.6744287791642 | | 1996 | 2.7064736951467 | | 1995 | 2.8093665377808 | | 1994 | 2.8799884110911 | | 1993 | 2.9418424812866 | | 1992 | 3.036790519215 | | 1991 | 3.2116520189554 | | 1990 | 3.4008316911418 | | 1989 | 3.4614365768542 | | 1988 | 3.5009890522739 | | 1987 | 3.5148001899179 | | 1986 | 3.5785874151975 | | 1985 | 3.659504455238 | | 1984 | 3.7139849024461 | | 1983 | 3.7092885164628 | | 1982 | 3.6587448682877 | | 1981 | 3.632683047606 | | 1980 | 3.5624723191008 | | 1979 | 3.4729905351676 | | 1978 | 3.4392803015393 | | 1977 | 3.3133044319875 | | 1976 | 3.2456343430403 | | 1975 | 3.3363340564836 | | 1974 | 3.4168934292709 | | 1973 | 3.4887453759725 | | 1972 | 3.5050835620283 | | 1971 | 3.6404696035591 | | 1970 | 3.8519662077225 | | 1969 | 3.932207386154 | | 1968 | 3.9669875179195 | | 1967 | 3.9844254011143 | | 1966 | 4.0109618871043 | | 1965 | 4.0062561069371 | | 1964 | 3.9474851960976 | | 1963 | 3.9114808813315 | | 1962 | 3.8528569647371 | | 1961 | 3.7479768802739 |
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