Year	number
2004	6.561643835616438
2005	6.5
2006	6.494252873563219
2007	6.494252873563219
2008	6.32183908045977
2009	6.215909090909091
2010	6.168539325842697
2011	6.146067415730337
2012	6.177777777777778
2013	6.322244897959184
2014	6.281428571428572
2015	6.210000000000001
2016	6.210000000000001
2017	6.224897959183673
2018	6.175918367346939
2019	6.20295918367347