Year	Number
1970	19.24521
1971	19.00165
1972	18.77662
1973	18.96393
1974	19.10151
1975	18.22059
1976	18.07052
1977	18.45777
1979	18.51625
1980	20.23058
1981	20.23262
1982	20.32281
1984	20.27509
1985	19.97819
1986	20.00797
1987	19.45186
1988	19.25796
1994	17.53274
1996	16.73337
1997	16.66847
1998	19.92697
1999	21.77841
2000	20.05203
2001	18.02999
2002	17.596
2004	17.95223
2005	17.44373
2006	17.1849
2007	16.36028
2008	17.22969