| Year | Value | | 2022 | 44.152090253493 | | 2021 | 43.653767645212 | | 2020 | 43.160587650174 | | 2019 | 42.671964095846 | | 2018 | 42.187884016277 | | 2017 | 41.710551606058 | | 2016 | 41.239016083733 | | 2015 | 40.766840102098 | | 2014 | 40.296695706356 | | 2013 | 39.832060812844 | | 2012 | 39.374727098961 | | 2011 | 38.922826113995 | | 2010 | 38.450768024574 | | 2009 | 37.963504385189 | | 2008 | 37.491545556752 | | 2007 | 37.024542824178 | | 2006 | 36.563129206016 | | 2005 | 36.108521925865 | | 2004 | 35.660315649201 | | 2003 | 35.217388382324 | | 2002 | 34.778166482715 | | 2001 | 34.330932625418 | | 2000 | 33.887849734781 | | 1999 | 33.540554631149 | | 1998 | 33.199087026204 | | 1997 | 32.838858395444 | | 1996 | 32.47004505 | | 1995 | 32.100147134998 | | 1994 | 31.734812898963 | | 1993 | 31.370363132627 | | 1992 | 31.004312115488 | | 1991 | 30.629292956646 | | 1990 | 30.258171166362 | | 1989 | 29.769310679007 | | 1988 | 29.31234162453 | | 1987 | 28.872879779584 | | 1986 | 28.427583445024 | | 1985 | 27.986449464535 | | 1984 | 27.553545582712 | | 1983 | 27.123998319318 | | 1982 | 26.701873155613 | | 1981 | 26.287287678394 | | 1980 | 25.847732373663 | | 1979 | 25.478581348477 | | 1978 | 25.055676579337 | | 1977 | 24.620180799193 | | 1976 | 24.190247267797 | | 1975 | 23.738892959272 | | 1974 | 23.288989794133 | | 1973 | 22.84419823501 | | 1972 | 22.413118619656 | | 1971 | 22.007068354702 | | 1970 | 21.591926949519 | | 1969 | 21.264001320149 | | 1968 | 20.951966075788 | | 1967 | 20.643055607865 | | 1966 | 20.339507323305 | | 1965 | 20.045345148928 | | 1964 | 19.756064070963 | | 1963 | 19.4696457907 | | 1962 | 19.188150360279 | | 1961 | 18.920450365268 | | 1960 | 18.600364124192 |
|