| Year | Value | | 2022 | 39.188938157682 | | 2021 | 39.044105640461 | | 2020 | 38.743394021343 | | 2019 | 38.343608565445 | | 2018 | 38.482135928852 | | 2017 | 39.199700162719 | | 2016 | 39.161158918353 | | 2015 | 40.157948476019 | | 2014 | 42.163141910429 | | 2013 | 42.719547798749 | | 2012 | 42.903787504091 | | 2011 | 43.108410932542 | | 2010 | 43.070427090709 | | 2009 | 42.731770134678 | | 2008 | 42.338349183117 | | 2007 | 41.895084868211 | | 2006 | 41.397912930009 | | 2005 | 40.952347294873 | | 2004 | 40.844799652284 | | 2003 | 40.997027845745 | | 2002 | 41.148374202145 | | 2001 | 41.300032033355 | | 2000 | 41.453852160912 | | 1999 | 41.611684502247 | | 1998 | 41.775301943784 | | 1997 | 41.947398419954 | | 1996 | 42.130477104099 | | 1995 | 42.440591050626 | | 1994 | 43.149315156973 | | 1993 | 44.129483655803 | | 1992 | 44.56733881144 | | 1991 | 44.476297125793 | | 1990 | 44.223189156852 | | 1989 | 44.018383602268 | | 1988 | 43.794034529224 | | 1987 | 43.554455334378 | | 1986 | 43.297394990989 | | 1985 | 43.152238647944 | | 1984 | 43.099395474938 | | 1983 | 43.064109565053 | | 1982 | 43.082881759019 | | 1981 | 43.104373354287 | | 1980 | 43.235087390469 | | 1979 | 43.534220890399 | | 1978 | 43.930887219222 | | 1977 | 44.392310930265 | | 1976 | 44.896136263883 | | 1975 | 45.084662563253 | | 1974 | 44.910648605528 | | 1973 | 44.722403395269 | | 1972 | 44.518787242075 | | 1971 | 44.294857313208 | | 1970 | 43.961279842947 | | 1969 | 43.468892824651 | | 1968 | 42.869580409827 | | 1967 | 42.177766474256 | | 1966 | 41.400586775793 | | 1965 | 40.923633815974 | | 1964 | 40.83087850082 | | 1963 | 40.752781252527 | | 1962 | 40.688807213306 | | 1961 | 40.723644895304 | | 1960 | 40.865379892933 |
|