Year	number
2005	14.75
2006	15.214285714285714
2007	15.178571428571429
2008	15.25
2009	15.142857142857142
2010	15.321428571428571
2011	15.03448275862069
2012	14.89655172413793
2013	15.105483870967744
2014	15.20225806451613
2015	15.266774193548388
2016	15.299032258064518
2017	15.299032258064518
2018	15.23451612903226
2019	15.105483870967744