| Year | Value | | 2022 | 2.9254868415296 | | 2021 | 2.8082695277977 | | 2020 | 3.0134189589789 | | 2019 | 2.1354044878119 | | 2018 | 2.2950112132584 | | 2017 | 2.1972571180267 | | 2016 | 3.0364737348825 | | 2015 | 2.0188218452279 | | 2014 | 2.8065140058069 | | 2013 | 5.5923130548489 | | 2011 | 5.0100968165946 | | 2010 | 5.7649328772799 | | 2009 | 7.9556617222537 | | 2008 | 5.8851522638061 | | 2007 | 4.4859487577169 | | 2006 | 2.9956265394013 | | 2005 | 0.83197797006471 | | 2004 | 1.011624972815 | | 2003 | 1.3225227287756 | | 2002 | 1.5244748375541 | | 2001 | 1.3540216558839 | | 2000 | 1.3620450030422 | | 1999 | 1.3652238332099 | | 1998 | 0.92295734965511 | | 1997 | 1.0758651286602 | | 1996 | 1.5446363415227 | | 1995 | 1.3856172925038 | | 1994 | 1.8775759426042 | | 1993 | 2.6792179580015 | | 1992 | 1.877133105802 | | 1990 | 1.9750739332488 | | 1989 | 3.9352864013992 | | 1988 | 5.2536231884058 | | 1987 | 2.9453817557907 | | 1986 | 4.5700378583018 | | 1985 | 3.6630036630037 | | 1984 | 4.3575697211155 | | 1983 | 4.7288776796973 |
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