Year	number
2005	15.458333333333334
2006	15.8
2007	15.84
2008	15.44
2009	15.12
2010	15.08
2011	15.36
2012	15.5
2013	14.950000000000001
2014	15.053448275862069
2015	15.053448275862069
2016	15.087931034482759
2017	15
2018	14.632758620689655
2019	14.241379310344827