Year	Number
1970	19.89662
1971	19.9215
1972	19.71699
1973	19.72596
1974	19.96554
1975	20.23242
1976	20.3532
1977	20.44524
1978	20.587
1979	20.58799
1980	20.74693
1981	20.66929
1982	20.93393
1983	20.78144
1984	20.88774
1985	20.79687
1986	20.87202
1987	20.68664
1988	20.61955
1989	20.78462
1990	20.71399
1991	21.0322
1992	21.46075
1993	21.91825
1994	22.22826
1995	22.46035
1996	22.61316
1997	22.80091
1998	23.11657
1999	23.26303
2000	23.36436
2001	23.53548
2002	23.23858
2003	23.24171
2004	23.36676
2005	22.52327
2006	21.98053
2007	21.62487
2008	20.99556
2009	20.53626
2010	20.53655
2011	21.22642
2012	21.49801
2013	22.61324
2014	22.76992
2015	22.50503
2016	21.60483
2017	21.33877
2018	21.40841