Year	Number
1970	35.28892
1971	35.83718
1972	36.29117
1973	35.92162
1974	35.98342
1975	35.31959
1976	35.40259
1977	34.54184
1978	36.24007
1979	39.66018
1980	36.70046
1981	39.02525
1982	37.46715
1983	37.09839
1984	38.47048
1986	39.08991
1990	34.82305
1991	38.05488
1992	35.88667
1993	37.28595
1994	34.89965
1995	34.78818
1996	32.9513
1997	33.13537
1998	32.82948
1999	31.72588
2000	34.05898
2004	32.90479
2005	29.14181
2006	27.92893
2008	33.34365
2009	33.87645
2015	29.14566
2016	28.37057
2017	25.59773