| Year | Value | | 2022 | 2.0371576186368 | | 2021 | 1.4845411173647 | | 2020 | 1.4388993659693 | | 2019 | 1.4451356816375 | | 2018 | 1.6368142046853 | | 2017 | 1.7681225057444 | | 2016 | 1.8820538100304 | | 2015 | 2.517735344605 | | 2014 | 2.2402195136191 | | 2013 | 2.3496068435151 | | 2012 | 2.2865982267456 | | 2004 | 2.2285644098019 | | 2003 | 2.441181414862 | | 2002 | 3.3246802439883 | | 2001 | 3.1002105461516 | | 2000 | 1.5346375140325 | | 1999 | 1.5951311433113 | | 1998 | 1.2549918031236 | | 1997 | 1.1728192620361 | | 1994 | 1.3561169045421 | | 1993 | 1.3407093629396 | | 1992 | 1.6946406146617 | | 1991 | 2.380554259916 | | 1982 | 0.6391086375341 | | 1981 | 0.79382834544523 | | 1980 | 0.90235764598238 |
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