Year	Number
1998	16.99718
1999	21.82106
2000	20.73776
2001	22.07713
2002	24.2948
2003	27.47752
2004	26.39423
2005	28.26191
2006	27.19545
2008	24.54058
2009	24.52325
2010	21.35018
2011	21.13719
2012	19.85683
2013	18.61689
2014	19.03446
2015	19.26979
2016	19.4292
2017	20.01707
2018	20.01815