Year	number
2005	15.51923076923077
2006	15.641509433962264
2007	15.735849056603774
2008	14.754716981132075
2009	14.87037037037037
2010	14.981481481481481
2011	15
2012	15.125
2013	15.281785714285714
2014	15.38892857142857
2015	15.442499999999999
2016	15.68690909090909
2017	15.596
2018	15.541454545454545
2019	15.559636363636363