Year	Number
1989	24.59917
1991	18.02169
1992	16.85162
1993	14.83037
1994	13.96353
1995	13.32718
1996	12.85426
1997	12.57169
1998	12.64793
1999	12.51326
2000	12.83862
2001	13.13507
2002	12.79369
2003	13.47478
2004	13.66506
2005	12.9349
2006	12.8368
2007	12.7049
2008	12.72627
2009	12.39015
2010	12.47651
2011	12.96035
2012	12.75412
2013	12.81445
2014	12.26841
2015	12.09628
2016	12.11967
2017	12.07981