Year	Number
1998	30.00112
1999	31.50241
2000	31.65343
2001	29.99204
2002	27.3953
2003	25.81195
2004	21.19574
2005	19.18166
2006	21.3636
2007	21.42344
2008	24.2615
2009	26.12235
2010	25.77661
2011	28.09058
2012	30.15118
2013	33.24147
2016	31.90002
2017	31.18447
2018	28.66906