Year	number
2005	15.465116279069768
2006	15.454545454545455
2007	15.431818181818182
2008	14.5
2009	14.636363636363637
2010	14.772727272727273
2011	14.681818181818182
2012	14.844444444444445
2013	15.06695652173913
2014	15.197391304347825
2015	15.306086956521737
2016	15.393043478260868
2017	15.267608695652173
2018	15.180652173913042
2019	15.137173913043478