Year	Number
1971	19.76149
1974	19.25364
1976	19.37154
1977	19.22805
1978	19.41801
1979	19.00156
1980	19.49122
1981	18.13735
1982	18.1932
1984	18.55194
1985	16.82338
1986	16.52609
1993	12.35322
1994	12.13049
2005	11.4904
2008	11.179
2009	11.14094
2010	11.03429
2011	11.18924
2012	11.20289
2013	11.14292
2014	11.23947
2015	11.23127
2016	11.30569
2017	11.27695