Year	Number
1971	6.1
1972	5.13333
1973	5.48
1974	10.9
1975	5.12745
1976	6.42771
1978	13.13978
1979	11.08621
1983	10.6782
1984	10.22823
1991	14.01809
1993	16.11152
1994	15.43783
1995	21.53075
1996	29.80317
1997	25.31534
1999	12.77878
2002	19.25031
2005	14.08367
2007	17.74072
2008	18.6098
2009	18.92127
2010	17.71063
2011	17.27499
2012	18.76709
2013	19.61859
2014	19.73162
2015	18.34496
2016	19.2185
2017	19.47238
2018	17.32014