Year	Number
1998	22.45961
1999	22.10281
2000	21.517
2001	21.58509
2002	21.18031
2003	20.22806
2004	19.95459
2005	19.37878
2006	19.12691
2007	18.28429
2008	17.27699
2009	16.39845
2010	15.93884
2012	15.15012
2013	15.57295
2014	15.168
2015	14.40654
2017	14.91335