Year	number
2005	15.630434782608695
2006	15.608695652173912
2007	15.717391304347826
2008	15.521739130434783
2009	15.5
2010	15.73913043478261
2011	15.695652173913043
2012	15.659574468085106
2013	16.30705882352941
2014	16.385490196078432
2015	16.476666666666667
2016	16.555098039215686
2017	16.2978431372549
2018	16.047647058823525
2019	15.919607843137252