| Year | Value | | 2020 | 4.6613527245607 | | 2019 | 4.3015686386969 | | 2018 | 4.5123056237577 | | 2017 | 4.4678926067547 | | 2016 | 4.4852730433229 | | 2015 | 4.5253456913451 | | 2014 | 4.6484823735502 | | 2013 | 4.8697793806024 | | 2012 | 4.8842692844425 | | 2011 | 5.0222040796131 | | 2010 | 5.4200497100249 | | 2009 | 5.5060880424602 | | 2008 | 6.2650622538353 | | 2007 | 6.3091217281946 | | 2006 | 6.7683040322171 |
|