Year	Number
1972	18.05
1973	20.2246
1974	31.9084
1976	15.22559
1977	16.28777
1982	15.59006
1983	16.93464
1984	15.63063
1990	18.53207
1992	18.3249
1993	18.55914
1997	17.23314
1999	17.70852
2000	17.77305
2001	17.35422
2002	17.94789
2003	16.35642
2004	15.82064
2005	16.93275
2006	17.0142
2007	16.69901
2008	16.35751
2009	16.2016
2010	15.70294
2011	15.31698
2012	14.33398
2013	12.17938
2014	12.76199
2015	11.73623
2016	11.78644
2017	11.41776
2018	11.14556