Year	Number
1991	19.78412
1992	19.81668
1993	19.5759
1994	18.8577
1995	18.98289
1996	20.16771
1997	20.00307
1998	19.2807
1999	18.77911
2000	18.68574
2001	17.12015
2002	16.1852
2003	15.26139
2004	14.27144
2005	13.44831
2006	12.496
2007	11.61559
2008	11.29601
2009	11.08342
2010	11.04222
2011	11.16445
2012	11.92302
2013	12.14857
2014	12.62333
2015	13.49787
2016	15.48619
2017	15.458
2018	15.42982