Year	number
2005	17.294117647058822
2006	17.176470588235293
2007	17.05263157894737
2008	17.157894736842106
2009	16.57894736842105
2010	16.42105263157895
2011	16.2
2012	16.1
2013	15.842105263157896
2014	15.947368421052632
2015	15.631578947368421
2016	16
2017	16.055555555555557
2018	16.055555555555557
2019	15.5