Year	Number
1970	33.97709
1971	34.70653
1972	32.59304
1973	32.08132
1974	33.33824
1975	33.94596
1976	34.83689
1977	35.00071
1978	35.33496
1979	33.5835
1980	33.89665
1981	34.75408
1982	36.3929
1983	35.16441
1984	33.8186
1985	34.46536
1986	30.13117
1987	31.64314
1988	31.9874
1989	29.06809
1990	29.3527
1991	32.9232
1992	27.68737
1993	29.10576
1994	33.19221
1995	35.19818
1996	37.62231
1997	59.42568
1998	58.51028
1999	57.3049
2000	59.42965
2001	54.32167
2002	52.72399
2003	52.38955
2004	50.08651
2005	51.73179
2006	49.04733
2007	49.56387
2008	49.92589
2009	49.28122
2010	48.576
2011	47.77601
2012	48.80484
2013	45.59109
2015	42.9168
2016	42.72062
2017	42.65911