Year	Number
1993	17.34015
1994	17.70224
1995	18.04026
1996	18.60775
1997	18.58851
1998	18.10733
1999	18.55962
2000	18.64903
2001	18.83275
2002	18.76386
2003	18.93788
2004	18.90834
2005	18.60626
2006	18.30713
2007	18.17956
2008	17.83815
2009	17.55004
2010	17.62234
2011	17.79098
2012	17.86417
2013	17.47601
2014	17.37316
2015	17.26269
2016	16.8994
2017	16.78126
2018	16.87411