Year	number
2005	43.535714285714285
2006	41.57142857142857
2007	41.464285714285715
2008	38.17857142857143
2009	37.285714285714285
2010	37.214285714285715
2011	35.172413793103445
2012	33.241379310344826
2013	30.69709677419355
2014	30.43903225806452
2015	30.051935483870967
2016	28.92290322580645
2017	27.955161290322582
2018	27.31
2019	28.148709677419355