Year	Number
1981	15.38462
1987	16.15385
1990	18.84615
1991	17.76129
1992	19.11765
1993	19.1875
1994	17.96591
1995	17.42632
1996	18.26519
1997	18.13514
1999	18.54082
2000	18.99485
2001	17.68571
2003	17.63084
2004	16.95946
2005	17.23437
2006	17.23759
2007	17.12371
2008	16.66954
2009	15.96296
2010	17.44974
2011	16.31719
2012	16.3211
2013	16.97248
2014	16.59513
2015	16.49451
2016	16.89135
2017	16.3978
2018	16.44072