Year	number
2005	15.029850746268657
2006	15.161764705882353
2007	15.235294117647058
2008	14.514705882352942
2009	14.652173913043478
2010	14.81159420289855
2011	14.81159420289855
2012	15.014084507042254
2013	15.236438356164383
2014	15.346027397260274
2015	15.423424657534245
2016	15.609861111111108
2017	15.460277777777776
2018	15.41861111111111
2019	15.40472222222222