Year	number
2005	16.7
2006	16.571428571428573
2007	16.582417582417584
2008	16.516483516483518
2009	16.42391304347826
2010	16.380434782608695
2011	16.153846153846153
2012	16.195652173913043
2013	16.224800000000002
2014	16.351287128712872
2015	16.2313
2016	16.17950495049505
2017	16.054059405940592
2018	15.67376237623762
2019	15.338316831683168