Year	number
2005	16.65765765765766
2006	16.539823008849556
2007	16.548672566371682
2008	16.141592920353983
2009	16.087719298245613
2010	16.05263157894737
2011	15.876106194690266
2012	15.965217391304348
2013	15.995737704918035
2014	16.125853658536585
2015	16.033852459016394
2016	16.058442622950817
2017	15.954590163934425
2018	15.639754098360655
2019	15.37844262295082