Year	Number
1971	27.81418
1972	28.4159
1973	27.40954
1974	24.59063
1975	22.90927
1976	23.01802
1977	21.79276
1978	19.61058
1979	20.40426
1980	20.21191
1981	19.24176
1982	19.27796
1983	19.17612
1984	18.90621
1985	18.40731
1986	18.12755
1987	17.35806
1988	17.12958
1989	17.80808
1990	17.31576
1991	17.07726
1992	16.94076
1993	17.50111
1994	18.44015
1995	18.00927
1999	18.75247
2000	18.9929
2001	18.82918
2002	20.06534
2004	17.5787
2005	17.24309
2006	16.87683
2007	16.16369
2008	15.17504
2009	13.85534
2010	13.28804
2011	13.62495