Year	Number
1971	22.2899
1972	22.35
1973	23.43308
1974	19.50751
1975	25.42559
1976	23.21641
1977	22.62767
1978	21.64695
1979	23.50629
1980	22.87041
1981	23.64977
1982	22.03707
1983	19.05444
1984	18.06385
1985	18.64175
1986	17.48572
1987	17.07381
1988	16.74497
1989	18.28449
1991	17.62592
1993	19.0113
1996	17.56331
1999	14.83547
2000	14.8221
2003	14.76242
2004	15.50997
2007	15.06209