Year	Number
1971	33.04378
1972	32.23735
1973	32.17553
1974	31.88956
1975	31.30267
1976	31.09508
1977	30.8129
1978	30.138
1979	30.21287
1980	30.05414
1981	30.11986
1982	30.06734
1983	27.77275
1984	27.78323
1985	27.32888
1986	27.56664
1987	27.47756
1988	27.22594
1989	27.00434
1991	26.8941
1992	26.66898
1993	26.69638
1994	25.36665
1996	23.72998
1998	21.63416
1999	21.7
2000	21.50002
2001	21.09928
2002	20.16689
2003	19.76984
2004	18.7644
2005	18.347
2006	17.759
2007	16.94053
2008	16.54729
2009	15.8539
2010	15.16485
2011	14.79974
2012	14.43462
2013	13.99258
2014	13.84932
2015	13.66248
2016	13.67502
2017	13.76886
2018	13.34788