Year	Number
1971	25.00341
1972	27.33701
1973	28.94357
1974	32.31153
1975	36.26592
1976	39.41493
1977	37.56085
1978	40.41439
1979	42.34177
1980	39.75567
1982	30.1843
1983	26.83776
1984	22.76032
1986	22.32131
1987	22.26266
1988	26.38089
1989	24.94189
1990	28.04832
1991	27.94858
1994	38.30316
1995	31.63771
1996	31.44943
1999	35.17028
2000	31.53444
2003	33.76439
2004	34.03618
2005	30.50532
2006	38.86003
2007	35.50651
2011	26.24584