Year	Number
1971	34.46686
1972	33.39772
1973	32.87038
1974	31.63394
1975	30.90816
1976	30.75769
1977	29.3721
1978	28.58133
1979	27.99918
1980	25.88282
1981	23.8559
1982	23.01315
1983	22.58083
1984	22.69793
1985	22.22969
1986	22.06739
1987	22.97254
1988	23.77882
1989	24.67714
1991	25.95905
1992	26.13592
1993	25.76566
1994	27.04757
1996	25.49342
1997	24.76132
1999	21.32821
2000	20.75006
2001	19.75159
2002	19.6154
2003	18.50138
2004	17.51665
2005	16.54586
2007	15.93954
2008	17.15784
2009	17.57943