| Year | Value | | 2021 | 30.59315177511 | | 2020 | 30.887916317182 | | 2019 | 31.202323335029 | | 2018 | 31.449096836433 | | 2017 | 31.714033100805 | | 2016 | 32.105742057078 | | 2015 | 32.460081640211 | | 2014 | 32.850534319603 | | 2013 | 33.271388206542 | | 2012 | 33.634248700685 | | 2011 | 34.045131535315 | | 2010 | 34.450314982047 | | 2009 | 34.817894541312 | | 2008 | 35.14848733928 | | 2007 | 35.455680162428 | | 2006 | 35.641118619559 | | 2005 | 35.94025994868 | | 2004 | 36.320770912299 | | 2003 | 36.677124066143 | | 2002 | 37.091817231852 | | 2001 | 37.373724157543 | | 2000 | 37.639650324754 | | 1999 | 37.955284809034 | | 1998 | 38.198153278264 | | 1997 | 38.635919251154 | | 1996 | 39.058868609278 | | 1995 | 39.543427895348 | | 1994 | 39.889331385385 | | 1993 | 40.304925610454 | | 1992 | 40.766625026474 | | 1991 | 41.244676458179 | | 1990 | 41.70479430581 | | 1989 | 42.143237806728 | | 1988 | 42.522239943167 | | 1987 | 43.044266169956 | | 1986 | 43.462925101692 | | 1985 | 43.875454293565 | | 1984 | 44.238305072695 | | 1983 | 44.539511505937 | | 1982 | 44.795313339378 | | 1981 | 44.954396528809 | | 1980 | 45.024353482343 | | 1979 | 45.102808461314 | | 1978 | 45.082541166387 | | 1977 | 45.108789500315 | | 1976 | 45.184710389999 | | 1975 | 45.280742080927 | | 1974 | 45.41987658697 | | 1973 | 45.579210075092 | | 1972 | 45.817580269698 | | 1971 | 45.935614718464 | | 1970 | 45.955813137182 | | 1969 | 46.035666103203 | | 1968 | 46.161396512204 | | 1967 | 46.330450510093 | | 1966 | 46.441675997565 | | 1965 | 46.636440437288 | | 1964 | 46.816266818616 | | 1963 | 46.978323622468 | | 1962 | 47.157474995908 | | 1961 | 47.197804097205 | | 1960 | 47.219498679585 |
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