Year	Number
1998	29.2579
1999	28.65016
2000	27.62088
2001	26.32162
2002	25.71566
2003	24.74851
2004	23.53538
2005	22.6083
2006	21.05867
2007	20.0195
2008	18.73162
2009	17.59008
2010	16.60995
2011	15.88789
2012	15.79127
2013	15.43995
2014	15.62477
2015	16.3117
2016	16.38986
2017	16.83703
2018	17.5546