2017 29.9608058608059
2016 30.0631147540984
2015 31.0220408163265
2014 30.0153424657534
2013 29.9446991404011
2012 30.2650273224044
2011 29.8046575342466
2010 30.6249315068493
2009 30.1616438356164
2008 29.7612021857923
2007 30.4404929577465
2006 30.3242424242424
2005 30.4006042296073
2004 30.0868098159509
2003 30.988785046729
2002 30.4483282674772
2001 31.0719402985075