Year	number
2005	15.75
2006	15.727272727272727
2007	15.727272727272727
2008	14.515151515151516
2009	14.696969696969697
2010	14.878787878787879
2011	14.696969696969697
2012	14.911764705882353
2013	15.087999999999997
2014	15.25942857142857
2015	15.345142857142855
2016	15.43085714285714
2017	15.265999999999998
2018	15.265999999999998
2019	15.265999999999998