Year	Number
1998	23.03823
1999	23.75769
2000	23.53216
2001	23.56226
2002	23.45077
2003	22.79853
2004	23.33801
2005	22.90231
2006	22.8986
2007	22.23652
2008	22.53792
2009	22.80656
2010	22.54554
2011	22.19451
2012	22.75019
2013	22.56219
2014	22.90423
2015	22.57762
2016	22.84262
2017	22.23453