Year	Number
1973	23.88316
1974	24.5222
1975	27.25157
1976	29.37366
1977	28.71103
1978	27.24839
1979	27.79299
1980	27.25454
1981	26.22991
1982	27.53168
1983	28.1906
1984	28.09199
1985	28.11877
1986	28.23198
1987	28.01195
1988	25.74566
1989	26.97376
1990	28.15169
1991	26.47804
1992	25.00408
1993	24.49797
1994	23.76627
1995	23.01232
1996	21.73318
1997	21.2319
1998	20.67739
1999	20.11765
2000	19.50682
2001	18.93774
2002	19.2024
2003	18.34976
2004	18.58476
2005	18.89326
2006	18.98018
2007	18.89748
2008	18.16095
2009	17.37778
2010	16.72863
2011	16.08595
2012	15.4374
2013	14.19647
2014	13.82142
2015	12.89505
2016	12.29765
2017	12.22449
2018	12.20815