| Year | Value | | 2021 | 10.294806401919 | | 2020 | 10.277057540506 | | 2019 | 10.269275104422 | | 2018 | 10.290589596007 | | 2017 | 10.299909833715 | | 2016 | 10.311698015247 | | 2015 | 10.318117913783 | | 2014 | 10.312640998991 | | 2013 | 10.303310508033 | | 2012 | 10.283009039071 | | 2011 | 10.276368351864 | | 2010 | 10.291755013674 | | 2009 | 10.289045839034 | | 2008 | 10.294706725425 | | 2007 | 10.315357765925 | | 2006 | 10.36323636078 | | 2005 | 10.33341238855 | | 2004 | 10.362652355341 | | 2003 | 10.37229677985 | | 2002 | 10.449173514132 | | 2001 | 10.517888663609 | | 2000 | 10.591274943014 | | 1999 | 10.728394364024 | | 1998 | 10.796476805258 | | 1997 | 10.910914962341 | | 1996 | 10.878913237669 | | 1995 | 11.017776578209 | | 1994 | 11.0565888494 | | 1993 | 11.104598537995 | | 1992 | 11.207764328998 | | 1991 | 32.069277042064 | | 1990 | 32.040631954697 | | 1989 | 32.291827336227 | | 1988 | 32.188264328052 | | 1987 | 32.367846991164 | | 1986 | 31.912830795672 | | 1985 | 31.943679351299 | | 1984 | 31.837912874865 | | 1983 | 30.95542383712 | | 1982 | 31.516206509045 | | 1981 | 32.936341801996 | | 1980 | 32.794218099288 | | 1979 | 33.336271291012 | | 1978 | 32.646585725933 | | 1977 | 32.589295551198 | | 1976 | 32.365643522905 | | 1975 | 32.421831963511 | | 1974 | 32.849304805764 | | 1973 | 33.284489786925 | | 1972 | 33.31754181081 | | 1971 | 32.655399598969 | | 1970 | 32.452680519137 | | 1969 | 32.940748738514 | | 1968 | 31.670449287178 | | 1967 | 31.36637066743 | | 1966 | 31.554767203578 | | 1965 | 31.364167199172 | | 1964 | 31.341030782452 | | 1963 | 31.369675869819 | | 1962 | 30.54117180442 | | 1961 | 30.514730185312 |
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