| Year | Value | | 2017 | 7.4422454661751 | | 2016 | 2.5781551524508 | | 2015 | -1.0539983197128 | | 2014 | 2.510876332537 | | 2013 | 0.77562932236745 | | 2012 | 1.1475385370605 | | 2011 | 6.2707530299569 | | 2010 | 3.5349123918983 | | 2009 | 1.4268597207054 | | 2008 | 10.446987512822 | | 2007 | 5.8422487490138 | | 2006 | 6.1491160645657 | | 2005 | 8.6656922113175 | | 2004 | 10.973405367955 | | 2003 | 11.638621958074 | | 2002 | 10.359060791851 | | 2001 | 8.2902831885033 | | 2000 | 6.3276355141116 | | 1999 | 4.4643546767589 | | 1998 | 3.2744455426047 | | 1997 | 2.1247313240804 | | 1996 | 2.9952802399114 | | 1995 | 1.4600063035097 | | 1994 | 1.0129520669486 | | 1993 | 0.96090446045919 | | 1992 | 7.9369801219287 | | 1991 | 10.595449399479 | | 1990 | 9.7098638456266 | | 1989 | 4.0736436479293 | | 1988 | 9.924023398104 | | 1987 | 4.685987787925 | | 1986 | 21.673874876889 | | 1985 | 16.765 | | 1984 | 0.1064516129037 | | 1983 | 9.8135531178777 | | 1982 | 10.837870380066 | | 1981 | 14.8992481203 | | 1980 | 22.393388916497 | | 1979 | 5.4600155279504 | | 1978 | 9.5843791211129 | | 1977 | 17.537938448461 | | 1976 | 7.1095758354755 |
|