Year | Value | 2021 | 16.734733940253 | 2020 | 14.861257673634 | 2019 | 15.199566531446 | 2018 | 15.536383732767 | 2017 | 14.493818534163 | 2016 | 13.981952981677 | 2015 | 13.158144339892 | 2014 | 13.241161663256 | 2013 | 13.630623437561 | 2012 | 14.077591497436 | 2011 | 13.850967631942 | 2010 | 13.436930293649 | 2009 | 13.650964447852 | 2008 | 14.495199990643 | 2007 | 14.817382703342 | 2006 | 13.727535211513 | 2005 | 13.313070435798 | 2004 | 12.966827829534 | 2003 | 13.693457572265 | 2002 | 13.248666789935 | 2001 | 13.548788416983 | 2000 | 14.261778076787 | 1999 | 12.791890310811 | 1998 | 12.620218746562 | 1997 | 12.901802171137 | 1996 | 13.234365058717 | 1995 | 12.992094991908 | 1994 | 12.687741581462 | 1993 | 12.499789803519 | 1992 | 12.730740849634 | 1991 | 12.535822379559 | 1990 | 13.419181256924 | 1989 | 12.835807572656 | 1988 | 13.37445811389 | 1987 | 13.456282693689 | 1986 | 13.238718347578 | 1985 | 13.499421874805 | 1984 | 13.894667730398 | 1983 | 14.80168213619 | 1982 | 14.696281503877 | 1981 | 14.652766872426 | 1980 | 14.663273346071 | 1979 | 14.745866805751 | 1978 | 14.554055934326 | 1977 | 14.133629978343 | 1976 | 14.461610745675 | 1975 | 13.211806214196 | 1974 | 11.57495256167 | 1973 | 10.475277260145 | 1972 | 11.153548749912 |
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