| Year | Value | | 2021 | 12.701723756297 | | 2020 | 12.414168424842 | | 2019 | 12.930632189379 | | 2018 | 13.47707569749 | | 2017 | 15.112682280159 | | 2016 | 14.223307208018 | | 2015 | 13.940077179899 | | 2014 | 15.47662196448 | | 2013 | 14.505282330373 | | 2012 | 16.409650328078 | | 1999 | 31.605377791285 | | 1998 | 33.535547370702 | | 1995 | 27.144617280148 | | 1994 | 23.914385676065 | | 1993 | 27.751307766635 | | 1992 | 28.162099724058 | | 1991 | 21.539754580602 | | 1990 | 20.807377549774 |
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