| Year | Value | | 2020 | 12.405134794463 | | 2019 | 12.647726167565 | | 2018 | 16.149924636118 | | 2017 | 18.027296536469 | | 2016 | 16.97414450315 | | 2015 | 14.347817458838 | | 2014 | 15.528471578996 | | 2013 | 16.79431650304 | | 2012 | 16.30216384392 | | 2011 | 24.128360719311 | | 2010 | 23.326508351427 | | 2009 | 23.058951887088 | | 2008 | 27.543152323693 | | 2007 | 24.081594309829 | | 2006 | 17.40589555266 | | 2005 | 16.777874320361 | | 2004 | 16.245650976319 | | 2003 | 19.364406230884 | | 2002 | 15.396238238059 | | 2001 | 16.192913936788 | | 1993 | 26.053712840173 | | 1992 | 28.685493917146 | | 1991 | 24.809283368758 | | 1990 | 28.742653987445 |
|