Year	Number
1972	19.55864
1976	18.06116
1982	18.15625
1987	17.74563
1991	19.68722
1994	20.30959
1998	19.99503
1999	19.75896
2000	18.58818
2001	18.9761
2002	17.28313
2003	17.55796
2004	17.22593
2007	17.07181
2008	16.95633
2009	16.96132
2010	16.27396
2012	15.748
2013	15.29101
2014	15.68575
2015	14.89632
2016	14.51432
2017	14.39337
2018	14.39258