Year	Number
1999	21.08124
2000	21.74679
2001	22.52288
2002	21.92847
2003	22.87617
2004	21.91879
2005	21.10308
2006	20.43732
2007	20.02474
2008	18.72611
2009	16.70788
2010	15.80228
2011	13.97291
2012	13.55749
2013	12.33689
2014	11.80369
2015	11.23579
2016	10.41041
2017	9.54474
2018	9.26008