Year	Number
1973	7.67857
1974	7
1975	7.59574
1976	7.31081
1977	7.28571
1978	6.81739
1979	5.07568
1980	5.0914
1981	6.40625
1982	6.41176
1983	7.93258
1984	7.6087
1985	9.11783
1987	9.5043
1989	11.06452
1992	19.45259
2004	14.87119
2005	14.87466
2006	10.23562
2008	12.8745
2009	12.06033
2010	11.27704
2012	12.33088
2015	15.0553
2016	14.84613
2017	15.29109
2018	14.69914