Year	number
2004	6.228571428571429
2005	6.20125786163522
2006	6.233128834355829
2007	6.216867469879518
2008	6.1017964071856285
2009	6.017857142857143
2010	5.952662721893491
2011	5.953216374269005
2012	5.988505747126437
2013	6.016108108108108
2014	5.972864864864865
2015	5.919247311827957
2016	5.93
2017	5.93247311827957
2018	5.923208556149732
2019	5.889251336898395