Year	Number
1970	23.27498
1971	26.65528
1972	22.65699
1973	27.10979
1975	23.43092
1976	21.69213
1977	21.55795
1978	19.68389
1979	20.06104
1980	19.74131
1981	21.4868
1982	18.47466
1983	17.93542
1986	17.81668
1995	18.43797
1996	18.26302
1999	24.00792
2000	24.01542
2001	25.04545
2002	27.23461
2007	32.81848
2009	31.69124
2010	30.23604