Year	number
2004	6.416666666666667
2005	6.348837209302325
2006	6.409090909090909
2007	6.409090909090909
2008	6.2727272727272725
2009	6.204545454545454
2010	6.181818181818182
2011	6.181818181818182
2012	6.222222222222222
2013	6.180652173913043
2014	6.115434782608696
2015	6.112978723404256
2016	6.155531914893617
2017	6.207872340425531
2018	6.186595744680851
2019	6.165319148936169