Year	number
2004	6.735294117647059
2005	6.594594594594595
2006	6.657894736842105
2007	6.605263157894737
2008	6.5
2009	6.394736842105263
2010	6.368421052631579
2011	6.368421052631579
2012	6.368421052631579
2013	6.2105263157894735
2014	6.131578947368421
2015	6.128205128205129
2016	6.17948717948718
2017	6.205128205128205
2018	6.17948717948718
2019	6.128205128205129