| Year | Value | | 2021 | 5.7373235753542 | | 2020 | 5.7801453135859 | | 2019 | 5.6452650731461 | | 2018 | 5.7285753661132 | | 2017 | 5.7265071028042 | | 2016 | 5.6181163739894 | | 2015 | 5.5541701861883 | | 2014 | 5.5456263725124 | | 2013 | 5.6064154305569 | | 2012 | 5.6212531823989 | | 2011 | 5.5955409846689 | | 2010 | 5.5950275885054 | | 2009 | 5.5920470207573 | | 2008 | 5.6231815173882 | | 2007 | 5.8829252065064 | | 2006 | 5.8539182812169 | | 2005 | 5.8104679229916 | | 2004 | 5.8512005580924 | | 2003 | 5.9037104150398 | | 2002 | 5.8315748489693 | | 2001 | 5.8037085981624 | | 2000 | 5.7394212708557 | | 1999 | 5.9544142833014 | | 1998 | 6.032864353524 | | 1997 | 6.0171002112463 | | 1996 | 6.1228375601867 | | 1995 | 6.1436026511059 | | 1994 | 6.1500299169129 | | 1993 | 6.2227618424006 | | 1992 | 6.107397783881 | | 1991 | 5.9940721476549 | | 1990 | 5.767763311638 | | 1989 | 5.7568423658656 | | 1988 | 5.7837051159541 | | 1987 | 5.7739873252244 | | 1986 | 5.7193594587653 | | 1985 | 5.6801412318919 | | 1984 | 5.6485075093071 | | 1983 | 5.589550598454 | | 1982 | 5.6125262322506 | | 1981 | 5.5371277449867 | | 1980 | 5.4461275760822 | | 1979 | 5.7233159878481 | | 1978 | 5.6269478964454 | | 1977 | 5.6994842629634 | | 1976 | 5.7732931973151 | | 1975 | 5.7897208911677 | | 1974 | 5.8612160658218 | | 1973 | 5.8870144864495 | | 1972 | 5.8120217770055 | | 1971 | 5.6910127047957 | | 1970 | 5.6189394237377 | | 1969 | 5.599850994565 | | 1968 | 5.5868940002175 | | 1967 | 5.6091059905275 | | 1966 | 5.5880508747128 | | 1965 | 5.6143119257564 | | 1964 | 5.5738213184204 | | 1963 | 5.5428170819461 | | 1962 | 5.529744400149 | | 1961 | 5.5405033329554 |
|