| Year | Value | | 2021 | 3.3365099269377 | | 2020 | 3.4251905972046 | | 2019 | 3.5117534942821 | | 2018 | 3.6014930114358 | | 2017 | 3.6936149936468 | | 2016 | 3.7873252858958 | | 2015 | 3.883418043202 | | 2014 | 3.9850698856417 | | 2013 | 4.0867217280813 | | 2012 | 4.188373570521 | | 2011 | 4.2900254129606 | | 2010 | 4.3916772554002 | | 2009 | 4.4570362134689 | | 2008 | 4.5223951715375 | | 2007 | 4.5877541296061 | | 2006 | 4.6531130876747 | | 2005 | 4.7184720457433 | | 2004 | 4.7838310038119 | | 2003 | 4.8491899618806 | | 2002 | 4.9145489199492 | | 2001 | 4.9799078780178 | | 2000 | 5.0452668360864 | | 1999 | 5.075206480305 | | 1998 | 5.1051461245235 | | 1997 | 5.1350857687421 | | 1996 | 5.1650254129606 | | 1995 | 5.1949650571792 | | 1994 | 5.2249047013977 | | 1993 | 5.2548443456163 | | 1992 | 5.2847839898348 | | 1991 | 5.3147236340534 | | 1990 | 5.3446632782719 |
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