Year	Number
1997	19.05174
1998	21.71288
1999	22.21903
2000	22.5921
2001	22.50996
2002	21.9465
2003	21.80427
2004	21.59708
2005	20.83153
2006	20.81578
2007	20.51878
2008	20.44826
2009	21.99327
2010	20.44218
2011	19.47237
2012	21.27085
2013	21.24489
2014	20.50339
2015	20.11378
2016	20.7907
2017	20.86742
2018	20.89568