| Year | Value | | 2022 | 50.467894995492 | | 2021 | 50.446386454966 | | 2020 | 50.423858373862 | | 2019 | 50.425213723237 | | 2018 | 50.449279925635 | | 2017 | 50.477148014992 | | 2016 | 50.508436811712 | | 2015 | 50.540486380963 | | 2014 | 50.573360266314 | | 2013 | 50.61037052605 | | 2012 | 50.651176823478 | | 2011 | 50.694210282301 | | 2010 | 50.715042381371 | | 2009 | 50.711835020371 | | 2008 | 50.708401656807 | | 2007 | 50.705668340099 | | 2006 | 50.705716854175 | | 2005 | 50.710777160791 | | 2004 | 50.718874006761 | | 2003 | 50.724347306113 | | 2002 | 50.721824732479 | | 2001 | 50.723470596933 | | 2000 | 50.741621344399 | | 1999 | 50.772568374565 | | 1998 | 50.804386462641 | | 1997 | 50.829482733647 | | 1996 | 50.850989332255 | | 1995 | 50.871270605859 | | 1994 | 50.890734168318 | | 1993 | 50.908878399994 | | 1992 | 50.928975507533 | | 1991 | 50.955158578415 | | 1990 | 50.98232955442 | | 1989 | 51.007141296299 | | 1988 | 51.02902290233 | | 1987 | 51.04639962873 | | 1986 | 51.064585962217 | | 1985 | 51.084211797543 | | 1984 | 51.100841613099 | | 1983 | 51.114906361459 | | 1982 | 51.124407285208 | | 1981 | 51.128046581831 | | 1980 | 51.124481161527 | | 1979 | 51.111766231928 | | 1978 | 51.088664221505 | | 1977 | 51.058350209924 | | 1976 | 51.030204512177 | | 1975 | 51.004061849593 | | 1974 | 50.979675521981 | | 1973 | 50.959110648518 | | 1972 | 50.948192722461 | | 1971 | 50.957064104407 | | 1970 | 50.983383602444 | | 1969 | 50.990046842269 | | 1968 | 50.952796376635 | | 1967 | 50.86902668656 | | 1966 | 50.752237308198 | | 1965 | 50.642585135351 | | 1964 | 50.567489260588 | | 1963 | 50.51411581976 | | 1962 | 50.458485451991 | | 1961 | 50.399512515193 | | 1960 | 50.34668741185 |
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