| Year | Value | | 2022 | 52.239156170344 | | 2021 | 52.252223259207 | | 2020 | 52.261935595269 | | 2019 | 52.276995559994 | | 2018 | 52.288651692751 | | 2017 | 52.303032298423 | | 2016 | 52.325427322115 | | 2015 | 52.353209326114 | | 2014 | 52.386929042091 | | 2013 | 52.432285840198 | | 2012 | 52.492186965349 | | 2011 | 52.563733007414 | | 2010 | 52.625007293308 | | 2009 | 52.667565713204 | | 2008 | 52.711679138989 | | 2007 | 52.757998439329 | | 2006 | 52.80301625564 | | 2005 | 52.847788253265 | | 2004 | 52.891399906259 | | 2003 | 52.934998398975 | | 2002 | 52.97493360969 | | 2001 | 52.985632749459 | | 2000 | 52.958497102125 | | 1999 | 52.883325882879 | | 1998 | 52.76552940528 | | 1997 | 52.631357241147 | | 1996 | 52.475715636551 | | 1995 | 52.310009064592 | | 1994 | 52.143964694657 | | 1993 | 51.967068687912 | | 1992 | 51.790160689154 | | 1991 | 51.727064148097 | | 1990 | 51.847524002021 | | 1989 | 52.046011691495 | | 1988 | 52.255321809259 | | 1987 | 52.452877099747 | | 1986 | 52.650203980715 | | 1985 | 52.853277579633 | | 1984 | 53.061411829503 | | 1983 | 53.161692759295 | | 1982 | 53.140378041115 | | 1981 | 53.119429590018 | | 1980 | 53.099909075498 | | 1979 | 53.07929235865 | | 1978 | 53.063159694694 | | 1977 | 53.045214217758 | | 1976 | 53.012970776684 | | 1975 | 52.966346529242 | | 1974 | 52.904170170357 | | 1973 | 52.838062144176 | | 1972 | 52.773784681969 | | 1971 | 52.722753168954 | | 1970 | 52.70393849683 | | 1969 | 52.663863700543 | | 1968 | 52.585463947142 | | 1967 | 52.506613434604 | | 1966 | 52.424317413182 | | 1965 | 52.343907182617 | | 1964 | 52.2739669985 | | 1963 | 52.253452871335 | | 1962 | 52.269856862195 | | 1961 | 52.294426171215 | | 1960 | 52.338187994651 |
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