Year	number
2005	17.181818181818183
2006	17.181818181818183
2007	17.363636363636363
2008	17.363636363636363
2009	17.272727272727273
2010	17.363636363636363
2011	17.454545454545453
2012	17.272727272727273
2013	17
2014	17
2015	17.272727272727273
2016	16.90909090909091
2017	16.90909090909091
2018	17
2019	17