| Year | Value | | 2022 | 37.49100237271 | | 2021 | 37.797138800841 | | 2020 | 38.107679330844 | | 2019 | 38.408875061105 | | 2018 | 38.70553223876 | | 2017 | 39.008239027559 | | 2016 | 39.311808236824 | | 2015 | 39.64334622057 | | 2014 | 40.050273015268 | | 2013 | 40.430576130085 | | 2012 | 40.754228550263 | | 2011 | 40.974697840049 | | 2010 | 41.195578130074 | | 2009 | 41.534720592837 | | 2008 | 41.880418566239 | | 2007 | 42.213242639419 | | 2006 | 42.547487528915 | | 2005 | 42.926584202047 | | 2004 | 43.311185209484 | | 2003 | 43.661636474923 | | 2002 | 43.999033448311 | | 2001 | 44.342571685524 | | 2000 | 44.705118598864 | | 1999 | 45.069504618756 | | 1998 | 45.432057076095 | | 1997 | 45.789728556742 | | 1996 | 46.128081538967 | | 1995 | 46.46153145362 | | 1994 | 46.814377543982 | | 1993 | 47.227744378493 | | 1992 | 47.652511260611 | | 1991 | 48.060954843988 | | 1990 | 48.401737508684 | | 1989 | 48.876493039893 | | 1988 | 49.214891777275 | | 1987 | 49.57682339725 | | 1986 | 50.028898354278 | | 1985 | 50.538651636898 | | 1984 | 51.04392792231 | | 1983 | 51.578364350699 | | 1982 | 52.109189212432 | | 1981 | 52.652536664059 | | 1980 | 53.206927928701 | | 1979 | 53.750200123911 | | 1978 | 54.230498475884 | | 1977 | 54.722561924167 | | 1976 | 55.335967955187 | | 1975 | 55.998001925216 | | 1974 | 56.622506071012 | | 1973 | 57.254340814483 | | 1972 | 57.90527491835 | | 1971 | 58.554674214767 | | 1970 | 59.192955650087 | | 1969 | 59.856257158198 | | 1968 | 60.518052517347 | | 1967 | 61.178296353254 | | 1966 | 61.817645439166 | | 1965 | 62.539584684947 | | 1964 | 63.310399712904 | | 1963 | 64.049106747135 | | 1962 | 64.779770748276 | | 1961 | 65.503685990439 | | 1960 | 66.223496053999 |
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