Year	Number
1970	32.95368
1971	32.8796
1972	32.53428
1973	33.37923
1974	32.17207
1975	32.28307
1976	31.54542
1977	30.8893
1978	31.82462
1979	31.42069
1980	30.71633
1981	30.2119
1982	29.48527
1983	26.16168
1984	26.01718
1985	25.52369
1986	25.62725
1987	27.00654
1988	27.27121
1989	24.4899
1990	26.35761
1991	26.55176
1992	26.23427
1993	25.91445
1994	26.44079
1995	25.94089
1996	26.38549
1997	25.32868
1998	25.29301
1999	24.95993
2000	24.4251
2001	23.92836
2002	23.727
2003	23.38881
2004	23.03334
2005	23.40661
2006	23.20169
2007	23.09878
2008	22.8901
2009	22.7445
2010	23.06935
2011	22.38783
2012	21.42142
2013	21.91546
2014	22.05643
2015	22.27264
2016	22.64947
2017	23.19498
2018	23.02361