| Year | Value | | 2022 | 3.6257410430448 | | 2021 | 0.60631938514085 | | 2020 | -2.3177062933138 | | 2019 | 1.0058200470214 | | 2018 | 2.0876693804698 | | 2017 | 1.3867183057641 | | 2016 | 2.7867934760204 | | 2015 | 1.8486274237498 | | 2014 | 2.6475532124619 | | 2013 | 3.3000115688844 | | 2012 | 2.7573966996298 | | 2011 | 0.40004069748808 | | 2010 | 1.9618846833462 | | 2009 | 2.7955128355041 | | 2008 | 3.5260031636372 | | 2007 | 3.256666666667 | | 2006 | 2.0074696545285 | | 2005 | 2.5862068965517 | | 2004 | 2.3529411764706 | | 2003 | 1.5936254980079 | | 2002 | 0.49554013875115 | | 2001 | -1.2075718015666 | | 2000 | 0.70485295309079 | | 1999 | -1.2875879718491 | | 1998 | 0.36653386454177 | | 1997 | 2.4315513395593 | | 1996 | 0.45222738253035 | | 1995 | 2.704034750647 | | 1994 | 0.81691089775978 | | 1993 | 2.5388601036269 | | 1992 | 0.17241379310331 | | 1991 | 0.76441973592761 | | 1990 | 0.92933543748909 | | 1989 | 1.4858973218257 | | 1988 | 0.30343596608658 | | 1987 | -1.7450017537706 | | 1986 | -2.2960932141956 | | 1985 | -2.6359693029697 | | 1984 | 0.32239925023533 | | 1983 | 2.9723991507507 | | 1982 | 8.8857130847146 | | 1981 | 11.344596808397 | | 1980 | 3.869525059415 | | 1979 | 2.2059919511677 | | 1978 | 15.785537594199 | | 1977 | 17.731120894237 | | 1976 | 22.495766575964 | | 1975 | 16.159782115371 | | 1974 | 24.39299830618 | | 1973 | 14.331826984998 | | 1972 | 5.0881953864881 | | 1971 | 5.789473684984 | | 1970 | 1.6289812783935 | | 1969 | 0.19412763892392 | | 1968 | 3.2573289902446 | | 1967 | 4.2580982230929 | | 1966 | 2.1344717185224 |
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