| Year | Value | | 2021 | 11.346157737807 | | 2020 | 10.870582808804 | | 2019 | 12.028272760243 | | 2018 | 12.346945709101 | | 2017 | 11.875941188496 | | 2016 | 11.652031387875 | | 2015 | 12.110969591461 | | 2014 | 12.285343811226 | | 2013 | 11.522116976453 | | 2012 | 11.344405604926 | | 1999 | 9.7070180791757 | | 1998 | 9.6945991361492 | | 1995 | 7.1836689710837 | | 1994 | 5.8984195225778 | | 1993 | 6.5500757877367 | | 1992 | 9.7537008862525 | | 1991 | 8.9051552447484 | | 1990 | 9.7673586197999 |
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