Year	Number
1971	24.81818
1972	25.86275
1973	23.84302
1974	20.5642
1975	17.90294
1976	21.22802
1977	19.89372
1978	17.6431
1980	19.26952
1981	17.49126
1983	17.82168
1984	16.19407
1985	16.43318
1986	14.29876
1999	8.36327
2002	9.56574
2006	8.94851