| Year | Value | | 2022 | 57.526246355866 | | 2021 | 57.672252937443 | | 2020 | 57.756619845346 | | 2019 | 57.803642360478 | | 2018 | 57.776493696887 | | 2017 | 57.706131122974 | | 2016 | 57.61537648706 | | 2015 | 57.507656422901 | | 2014 | 57.384255815404 | | 2013 | 57.024215927013 | | 2012 | 56.411612766715 | | 2011 | 55.764608482 | | 2010 | 55.083730899537 | | 2009 | 54.360712474609 | | 2008 | 53.591899858408 | | 2007 | 52.774309037112 | | 2006 | 52.002697192439 | | 2005 | 51.645831840478 | | 2004 | 51.63718205438 | | 2003 | 51.630072739262 | | 2002 | 51.628210918148 | | 2001 | 51.636480071278 | | 2000 | 51.64969363591 | | 1999 | 51.649880802989 | | 1998 | 51.635889494368 | | 1997 | 51.619090098127 | | 1996 | 51.604564870509 | | 1995 | 51.608393233362 | | 1994 | 51.657209923831 | | 1993 | 51.735849824076 | | 1992 | 51.816539542353 | | 1991 | 51.905664441094 | | 1990 | 52.006827971568 | | 1989 | 52.106342658658 | | 1988 | 52.199753741239 | | 1987 | 52.30348190506 | | 1986 | 52.427430599569 | | 1985 | 52.563516700546 | | 1984 | 52.659066750548 | | 1983 | 52.723055219445 | | 1982 | 52.798198518247 | | 1981 | 52.873637740698 | | 1980 | 52.947169879978 | | 1979 | 53.025710115639 | | 1978 | 53.11584681942 | | 1977 | 53.224148835248 | | 1976 | 53.34581061654 | | 1975 | 53.468272710758 | | 1974 | 53.563306080147 | | 1973 | 53.606047132059 | | 1972 | 53.621650507672 | | 1971 | 53.635905749768 | | 1970 | 53.643614647485 | | 1969 | 53.651029949234 | | 1968 | 53.658368447811 | | 1967 | 53.684238584769 | | 1966 | 53.754380800824 | | 1965 | 53.85306887516 | | 1964 | 53.981094615818 | | 1963 | 54.136168058719 | | 1962 | 54.300751567496 | | 1961 | 54.478882833788 | | 1960 | 54.657937806874 |
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