Year	number
2004	6.634408602150538
2005	6.555555555555555
2006	6.581818181818182
2007	6.572727272727272
2008	6.4
2009	6.2792792792792795
2010	6.241071428571429
2011	6.232142857142857
2012	6.2631578947368425
2013	6.324426229508197
2014	6.275245901639344
2015	6.207967479674796
2016	6.224227642276423
2017	6.244227642276423
2018	6.20520325203252
2019	6.210487804878048