| Year | Value | | 2022 | 1.4921185588243 | | 2021 | 1.5351396675707 | | 2020 | 1.622836376932 | | 2019 | 1.6806966845314 | | 2018 | 1.7097289071087 | | 2017 | 1.7398503801262 | | 2016 | 1.7733369368323 | | 2015 | 1.8093624065659 | | 2014 | 1.8486191060326 | | 2013 | 1.8959591468182 | | 2012 | 1.950842899197 | | 2011 | 2.0098680256265 | | 2010 | 2.0759779587677 | | 2009 | 2.1433649553816 | | 2008 | 2.2128989309949 | | 2007 | 2.2881134376519 | | 2006 | 2.3592107357765 | | 2005 | 2.4246004089444 | | 2004 | 2.4892943297726 | | 2003 | 2.5592129363433 | | 2002 | 2.62751491094 | | 2001 | 2.6847341563402 | | 2000 | 2.7313830002978 | | 1999 | 2.6409996391858 | | 1998 | 2.640957062521 | | 1997 | 2.7650746444425 | | 1996 | 2.7775590839606 | | 1995 | 2.7893185153559 | | 1994 | 2.8001138816217 | | 1993 | 2.8054302516019 | | 1992 | 2.8059468599597 | | 1991 | 2.8031358115635 | | 1990 | 2.8006096501523 | | 1989 | 2.797642988494 | | 1988 | 2.8096744067901 | | 1987 | 2.8418182070744 | | 1986 | 2.8727405407219 | | 1985 | 2.9084048094573 | | 1984 | 2.9559149503015 | | 1983 | 2.9961898711152 | | 1982 | 3.031585844239 | | 1981 | 3.0690499504681 | | 1980 | 3.0981713045403 | | 1979 | 3.1159149040664 | | 1978 | 3.125367909014 | | 1977 | 3.1380675298163 | | 1976 | 3.1429942349533 | | 1975 | 2.9867000629443 | | 1974 | 2.905600171463 | | 1973 | 3.0219853749137 | | 1972 | 3.0403188498418 | | 1971 | 3.0000193296289 | | 1970 | 2.9677601731173 | | 1969 | 2.9451285239838 | | 1968 | 2.9200530000933 | | 1967 | 2.9063658315288 | | 1966 | 2.9136204024731 | | 1965 | 2.9117137583925 | | 1964 | 2.9024678783601 | | 1963 | 2.9015837421077 | | 1962 | 2.8981608752359 | | 1961 | 2.9069414887468 |
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