Year	Number
1998	19.03853
1999	19.80951
2000	21.60781
2001	23.05601
2002	23.98631
2003	24.77323
2004	26.75999
2005	23.03941
2006	23.40961
2008	21.79133
2009	21.83711
2010	19.90979
2011	19.40707
2012	18.12275
2013	17.37462
2014	18.05856
2015	18.48722
2016	17.88309
2017	17.32903
2018	17.32894