Year	Number
1970	36.86409
1971	40.20145
1972	36.33756
1973	34.96495
1974	33.15202
1975	38.58511
1976	38.15592
1977	36.45236
1979	34.22583
1980	33.66303
1981	32.32296
1982	34.60921
1983	31.08843
1985	30.58888
1986	30.68912
1987	28.84975
1988	28.0241
1989	27.37077
1990	24.63115
1991	24.84802
1992	24.69884
1993	28.67781
1994	21.94724
1995	23.05377
1996	22.74264
1997	22.398
1998	29.47285
1999	38.78396
2000	27.82807
2001	28.2376
2002	26.75173
2003	25.06755
2004	24.60625
2005	24.73565
2006	22.793
2007	20.40715
2008	19.59269
2009	19.9382
2010	20.00387
2011	17.73656
2012	17.85078
2015	18.15347
2016	18.9531
2017	19.10868
2018	19.54931