Year	Number
1970	12.21845
1971	11.93067
1972	11.78657
1973	10.87732
1974	11.85968
1975	13.20096
1976	15.41762
1977	12.62235
1978	11.27321
1979	11.23661
1980	10.62254
1981	11.07534
1982	10.35542
1983	10.35187
1984	10.54858
1985	11.96827
1986	12.90108
1987	12.73912
1998	13.14669
1999	15.76137
2000	15.67528
2001	14.77395
2002	15.94887
2004	14.94705
2006	15.47501
2009	16.77677