Year	Number
1998	16.60159
1999	16.41782
2000	16.64514
2001	18.25312
2002	21.37926
2003	23.87917
2004	24.66877
2005	27.60043
2006	31.66317
2007	30.59806
2008	27.00738
2009	25.8658
2010	23.90656
2012	20.16037
2013	20.07371
2014	19.7956
2015	19.95644
2016	20.39486
2017	20.69476
2018	21.87195