| Year | Value | | 2022 | 55.040714354305 | | 2021 | 54.979910239221 | | 2020 | 54.893520406272 | | 2019 | 54.805108980282 | | 2018 | 54.698812680302 | | 2017 | 54.591200393559 | | 2016 | 54.485586225306 | | 2015 | 54.382954184246 | | 2014 | 54.284394431699 | | 2013 | 54.187672439197 | | 2012 | 54.094381010842 | | 2011 | 53.991702219479 | | 2010 | 53.871865425468 | | 2009 | 53.74790506751 | | 2008 | 53.623407490931 | | 2007 | 53.501655742108 | | 2006 | 53.381082879617 | | 2005 | 53.264849638001 | | 2004 | 53.161792647464 | | 2003 | 53.061734015282 | | 2002 | 52.952315866123 | | 2001 | 52.856804993596 | | 2000 | 52.776356681015 | | 1999 | 52.69473460947 | | 1998 | 52.618660412584 | | 1997 | 52.549597758526 | | 1996 | 52.478858091399 | | 1995 | 52.404551366897 | | 1994 | 52.263841055834 | | 1993 | 52.046553587734 | | 1992 | 51.761659842974 | | 1991 | 51.616403110212 | | 1990 | 51.66177005229 | | 1989 | 51.734941212568 | | 1988 | 51.787701101152 | | 1987 | 51.783602139308 | | 1986 | 51.765518087078 | | 1985 | 51.747101393076 | | 1984 | 51.738607170559 | | 1983 | 51.74111900382 | | 1982 | 51.749603608482 | | 1981 | 51.756697547505 | | 1980 | 51.763551222711 | | 1979 | 51.811170472106 | | 1978 | 51.830872246418 | | 1977 | 51.779938985467 | | 1976 | 51.73615678703 | | 1975 | 51.670518348536 | | 1974 | 51.572057987185 | | 1973 | 51.470822933799 | | 1972 | 51.368328670779 | | 1971 | 51.266942321327 | | 1970 | 51.219412107985 | | 1969 | 51.223873436767 | | 1968 | 51.227476876308 | | 1967 | 51.236016005114 | | 1966 | 51.251232849023 | | 1965 | 51.269644247155 | | 1964 | 51.29258982722 | | 1963 | 51.32355748093 | | 1962 | 51.35876893867 | | 1961 | 51.396935375064 | | 1960 | 51.441327039705 |
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