| Year | Value | | 2020 | 1.1171990069611 | | 2019 | 1.0908427290762 | | 2018 | 1.1068076910404 | | 2017 | 0.92145297082383 | | 2016 | 0.95851057868009 | | 2015 | 1.4189371410847 | | 2014 | 1.4086277107149 | | 2013 | 1.4064237587493 | | 2012 | 1.4181641340594 | | 2011 | 1.4231924402906 | | 2010 | 1.9177872232473 | | 2009 | 1.9154368993823 | | 2008 | 2.1511340922343 | | 2007 | 2.1848645981146 | | 2006 | 2.2257676227377 | | 2005 | 2.5892073309293 | | 2004 | 2.5344491270463 | | 2003 | 2.5579357398393 | | 2002 | 3.0171734329629 | | 2001 | 3.1904299713521 | | 2000 | 3.2898445562902 | | 1999 | 3.2605283158246 | | 1998 | 3.7848696831659 | | 1997 | 3.7200103336671 | | 1996 | 3.7129016988348 | | 1995 | 3.6136889408887 | | 1994 | 2.0975452951797 | | 1993 | 1.3459430945613 | | 1992 | 2.518295800551 | | 1991 | 2.7201407355057 |
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