Year	Number
1998	16.49306
1999	16.85595
2000	16.67216
2001	16.30242
2002	16.29502
2003	16.18667
2004	16.42459
2005	16.42004
2006	16.19416
2007	15.73683
2008	16.02428
2009	15.57821
2010	15.82366
2011	15.95947
2012	15.36293
2013	15.4833
2014	15.4702
2015	15.35302
2016	14.93421
2017	15.39276