Year | Mean | Minimum | Maximum | Year | Mean | Minimum | Maximum | Year | Mean | Minimum | Maximum |
1956 | 25.14 | 25.62 | 24.44 | 1976 | 24.75 | 25.97 | 23.53 | 1996 | 25.03 | 25.76 | 23.56 |
1957 | 24.92 | 25.61 | 24.16 | 1977 | 24.89 | 25.65 | 23.88 | 1997 | 24.77 | 25.84 | 23.49 |
1958 | 25.17 | 25.71 | 24.02 | 1978 | 25.17 | 25.68 | 24.51 | 1998 | 25.66 | 26.40 | 24.92 |
1959 | 24.87 | 25.86 | 23.89 | 1979 | 25.10 | 25.88 | 23.91 | 1999 | 25.01 | 25.60 | 23.99 |
1960 | 24.77 | 25.45 | 23.89 | 1980 | 25.20 | 25.88 | 24.16 | 2000 | 24.93 | 25.91 | 23.67 |
1961 | 24.64 | 25.51 | 23.72 | 1981 | 25.26 | 26.00 | 24.43 | 2001 | 25.16 | 26.12 | 23.73 |
1962 | 24.92 | 25.83 | 23.91 | 1982 | 24.92 | 26.12 | 23.59 | 2002 | 25.29 | 26.08 | 24.07 |
1963 | 24.76 | 25.64 | 23.40 | 1983 | 25.41 | 26.08 | 24.20 | 2003 | 25.41 | 26.32 | 24.20 |
1964 | 24.97 | 25.53 | 24.18 | 1984 | 25.13 | 26.02 | 23.93 | 2004 | 25.19 | 26.25 | 23.67 |
1965 | 24.38 | 25.25 | 22.70 | 1985 | 25.13 | 25.75 | 23.76 | 2005 | 25.22 | 26.06 | 23.93 |
1966 | 24.69 | 25.18 | 23.53 | 1986 | 25.26 | 25.92 | 24.39 | 2006 | 25.08 | 25.66 | 24.15 |
1967 | 24.60 | 25.43 | 23.74 | 1987 | 25.36 | 26.32 | 24.17 | 2007 | 25.09 | 25.84 | 23.75 |
1968 | 24.72 | 25.38 | 24.12 | 1988 | 25.52 | 26.22 | 24.65 | 2008 | 25.00 | 26.14 | 24.03 |
1969 | 24.95 | 25.62 | 24.11 | 1989 | 25.31 | 25.80 | 24.64 | 2009 | 25.32 | 25.82 | 24.55 |
1970 | 25.01 | 25.49 | 23.93 | 1990 | 25.35 | 26.25 | 24.23 | 2010 | 25.64 | 25.98 | 24.86 |
1971 | 24.97 | 25.80 | 23.94 | 1991 | 25.08 | 25.98 | 24.28 | 2011 | 25.02 | 25.94 | 24.14 |
1972 | 24.62 | 25.54 | 23.59 | 1992 | 25.42 | 26.04 | 24.29 | 2012 | 25.17 | 25.93 | 24.30 |
1973 | 25.22 | 25.82 | 24.15 | 1993 | 25.14 | 25.86 | 24.13 | 2013 | 25.34 | 25.90 | 24.38 |
1974 | 24.97 | 25.65 | 23.86 | 1994 | 25.10 | 26.05 | 24.11 | 2014 | 25.27 | 26.08 | 24.04 |
1975 | 24.96 | 25.40 | 24.16 | 1995 | 25.09 | 26.15 | 24.03 | 2015 | 25.38 | 25.81 | 24.35 |
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| 2016 | 25.70 | 26.28 | 24.54 |