Year	Number
1971	22.95673
1972	20.8089
1973	21.20776
1974	20.68463
1975	21.50105
1976	21.1362
1977	21.15275
1978	21.05421
1979	20.59057
1980	20.45939
1981	20.73225
1982	20.76904
1983	20.95349
1984	21.56076
1985	19.18788
1986	17.51512
1987	17.52066
1988	16.45152
2002	18.76206
2003	17.87835
2014	14.5993
2017	11.431
2018	12.26127