| Year | Value | | 2021 | 35.468076772425 | | 2020 | 34.978456717587 | | 2019 | 34.782608695652 | | 2018 | 34.90990990991 | | 2017 | 34.88053270662 | | 2016 | 34.802193497846 | | 2015 | 35.086173129651 | | 2014 | 34.958871915394 | | 2013 | 35.27222875049 | | 2012 | 35.487661574618 | | 2011 | 35.624755189973 | | 2010 | 35.624755189973 | | 2009 | 35.566000783392 | | 2008 | 35.115550332942 | | 2007 | 35.252643948296 | | 2006 | 35.546415981199 | | 2005 | 35.350567959264 | | 2004 | 35.683509596553 | | 2003 | 35.820603211908 | | 2002 | 35.761848805327 | | 2001 | 35.898942420682 | | 2000 | 36.036036036036 | | 1999 | 36.976106541324 | | 1998 | 37.504896200548 | | 1997 | 38.249118683901 | | 1996 | 39.071680376028 | | 1995 | 40.109674892284 | | 1994 | 41.030160595378 | | 1993 | 41.382687034861 | | 1992 | 42.303172737955 | | 1991 | 43.157422640031 | | 1990 | 43.059146102624 | | 1989 | 46.572659616138 | | 1988 | 48.237367802585 | | 1987 | 49.725812769291 | | 1986 | 51.155503329416 | | 1985 | 52.506854680768 | | 1984 | 53.819036427732 | | 1983 | 52.526439482961 | | 1982 | 52.467685076381 | | 1981 | 50.900900900901 | | 1980 | 49.275362318841 | | 1979 | 47.845671758715 | | 1978 | 46.220133176655 | | 1977 | 44.79044261653 | | 1976 | 43.184488836663 | | 1975 | 41.558950254602 | | 1974 | 40.109674892284 | | 1973 | 40.109674892284 | | 1972 | 36.95652173913 | | 1971 | 36.95652173913 | | 1970 | 36.349392871132 | | 1969 | 35.056795926361 | | 1968 | 33.607520564042 | | 1967 | 32.040736388563 | | 1966 | 32.021151586369 | | 1965 | 30.454367410889 | | 1964 | 29.083431257344 | | 1963 | 27.810419114767 | | 1962 | 27.614571092832 | | 1961 | 27.320799059929 |
|