Year	Number
1998	16.58858
1999	17.32423
2000	18.26418
2001	18.22594
2002	19.7351
2003	20.78361
2004	20.72588
2005	21.12879
2006	20.57922
2007	20.56849
2008	21.18239
2009	16.50547
2010	17.04933
2011	18.35603
2012	17.96082
2013	17.93554
2014	17.65478
2015	16.15062
2016	14.58063
2017	14.05817
2018	13.42825