Year	Number
1997	15.58429
1998	15.93703
1999	14.54446
2000	15.28654
2001	16.78283
2002	17.4728
2003	16.24633
2004	16.00798
2005	15.59412
2006	15.91425
2007	16.12794
2008	15.28906
2009	15.23407
2010	15.05505
2011	15.02039
2012	14.96061
2013	15.28136
2014	14.19848
2015	14.07743
2016	14.29422
2017	14.48186
2018	14.46047