Year	Number
1971	38.3669
1972	35.11194
1973	38.23693
1974	38.09809
1975	37.80729
1976	38.43186
1977	39.22867
1978	39.38769
1979	39.65434
1980	38.12973
1981	38.13212
1982	37.38594
1983	37.5
1984	35.29583
1985	34.30021
1986	32.91982
1987	30.86076
1988	29.51075
1989	28.50544
1990	28.26422
1991	25.86781
1992	24.78347
1993	23.73702
1994	22.81063
1996	21.36964