Year	Number
1972	11.06888
1973	12.56869
1974	16.71044
1976	18.63611
1977	15.66249
1978	16.20348
1982	17.66061
1983	15.69504
1984	14.16931
1985	14.58881
1986	14.02866
1987	15.21331
1989	18.68255
1990	17.7399
1991	21.81984
1992	21.88964
1993	21.7459
2003	18.84814
2004	21.21669
2005	22.82075
2006	28.40414
2007	27.98893
2009	26.52189
2010	29.94031
2011	29.38317
2012	29.70914
2013	31.66009
2014	37.21738
2015	35.79281
2016	32.13206
2017	28.02967
2018	26.59842