Year	number
2005	16.476190476190474
2006	16.40909090909091
2007	16.40909090909091
2008	14.590909090909092
2009	14.681818181818182
2010	14.681818181818182
2011	14.727272727272727
2012	15.043478260869565
2013	14.954545454545455
2014	15.090909090909092
2015	15.136363636363637
2016	15.476190476190476
2017	15.476190476190476
2018	15.476190476190476
2019	15.571428571428571