| Year | Value | | 2020 | 1.5636326474332 | | 2019 | 1.5346038109626 | | 2018 | 1.5317202730051 | | 2017 | 1.5311698819309 | | 2016 | 1.5388133154944 | | 2015 | 1.5497558243352 | | 2014 | 1.4827583862024 | | 2013 | 1.4308522629944 | | 2012 | 1.5351836743554 | | 2011 | 1.5186641416641 | | 2010 | 1.6031740664673 | | 2009 | 1.6478794853466 | | 2008 | 1.6650001526519 | | 2007 | 1.6791791264847 | | 2006 | 1.6841080066716 | | 2005 | 1.8056475048906 | | 2004 | 1.8041998456331 | | 2003 | 1.8704322910948 | | 2002 | 1.9204586465226 | | 2001 | 1.999865583558 | | 2000 | 2.1332457813393 | | 1999 | 2.2175155113672 | | 1998 | 2.4038410466747 | | 1997 | 2.4670917032793 | | 1996 | 2.354038550571 | | 1995 | 2.4331921822226 | | 1994 | 1.8954256948543 | | 1993 | 1.8853582581929 | | 1992 | 2.2457483744801 |
|