Year	Number
1999	25.09606
2000	28.36639
2001	26.93986
2002	25.75551
2003	26.16569
2004	27.59462
2005	26.62547
2006	27.86365
2007	25.10429
2008	24.20475
2009	23.3079
2010	22.50795
2011	20.49871
2012	20.18146
2013	19.86081
2014	19.71825
2015	19.9462
2016	19.64335
2017	20.08626
2018	17.33404