Year	Number
1970	36.41359
1971	36.2904
1972	36.52473
1973	37.3184
1974	37.21744
1975	37.0365
1976	37.23064
1977	38.28117
1978	37.85523
1979	37.79695
1980	38.03619
1981	37.89236
1982	37.67506
1983	36.80436
1984	36.29487
1985	35.90513
1986	35.6272
1987	35.50801
1988	35.42797
1989	34.5795
1990	35.12937
1991	35.09541
1992	35.07026
1993	34.9469
1994	35.01094
1995	34.75426
1996	34.46095
1997	34.16735
1998	34.00723
1999	34.06869
2000	34.287
2001	34.15999
2002	33.94949
2003	33.78044
2004	33.75974
2005	33.96956
2006	33.68613
2007	33.66571
2008	33.59626
2009	32.72449
2010	31.96993
2011	30.98056
2012	31.0889
2013	28.75672
2014	28.4329
2015	28.01515
2016	28.87083
2017	28.62456
2018	28.87235