Year | Value | 2021 | 15.032602737485 | 2020 | 13.569315734444 | 2019 | 13.748632089749 | 2018 | 14.225752351397 | 2017 | 13.714933092013 | 2016 | 13.788786992337 | 2015 | 14.199623037737 | 2014 | 14.135276891134 | 2013 | 13.611749848385 | 2012 | 11.762925951214 | 1994 | 15.106769212661 | 1993 | 14.88200609981 | 1992 | 16.021462364388 | 1991 | 15.776972519182 | 1990 | 15.710807422767 | 1989 | 16.727952697565 | 1988 | 15.39696129463 | 1987 | 15.565553821791 | 1986 | 14.430010413712 | 1985 | 12.585183496793 | 1984 | 10.589629576103 | 1983 | 10.638441930464 | 1982 | 9.2276456454178 | 1981 | 9.9680828341727 | 1980 | 9.6701977879166 | 1979 | 9.6701583885667 | 1978 | 9.4994955227719 | 1977 | 8.9004083940003 | 1976 | 9.0217894936787 | 1975 | 8.762149051131 | 1974 | 8.5808214530639 | 1973 | 9.320855203954 | 1972 | 8.9588034603857 |
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