Year	Number
1970	22.98313
1971	23.21685
1972	22.82934
1973	23.58892
1974	23.66369
1975	23.72165
1976	23.15936
1977	23.11947
1978	22.74639
1979	22.61981
1980	22.64032
1981	22.66357
1982	22.27246
1983	22.23387
1984	22.30377
1985	22.78396
1986	22.24856
1987	22.25505
1988	22.33561
1989	22.35006
1990	22.44861
1991	22.85457
1992	23.07391
1993	23.52354
1994	23.32105
1995	22.71852
1996	22.19352
1997	22.49396
1998	22.31775
1999	22.401
2000	23.30114
2001	23.14786
2002	23.23875
2003	23.3558
2004	23.01362
2005	23.1017
2006	23.33338
2007	23.38523
2008	23.12124
2009	23.33726
2010	23.5053
2011	23.62722
2012	22.86115
2013	23.27745
2014	22.71209
2015	23.90217
2016	23.02266
2017	23.17797
2018	23.07468