Year	Number
1997	15.42511
1998	15.65272
1999	14.24133
2000	15.00644
2001	16.51242
2002	17.16578
2003	15.94042
2004	15.78304
2005	15.37077
2006	15.71276
2007	15.96281
2008	15.12648
2009	15.11517
2010	14.94495
2011	14.939
2012	14.91743
2013	15.24264
2014	14.14376
2015	14.02718
2016	14.26408
2017	14.49758
2018	14.47577