Year	Number
1975	31.46942
1976	30.80377
1977	30.93917
1978	30.8313
1979	29.9845
1980	29.30819
1981	28.76056
1982	28.56332
1983	28.10116
1984	28.68513
1985	28.68803
1986	28.64214
1987	29.18524
1988	28.59807
1989	29.56776
1990	29.0985
1991	28.08016
1992	27.35053
1993	26.41704
1994	25.27908
1995	24.72714
1996	24.48892
1997	23.96206