Year	Number
1970	14.79804
1971	14.81115
1972	14.69181
1973	15.21397
1974	15.01289
1975	14.77264
1976	14.52998
1977	14.34878
1978	14.33293
1979	14.15808
1980	14.00067
1981	13.86248
1982	13.73277
1983	13.63993
1984	13.52485
1985	13.36573
1986	13.38032
1987	13.24881
1988	13.053
1989	12.91182
1990	12.55881
1991	12.33109
1992	12.24719
1993	12.22488
1994	12.36015
1995	12.70879
1996	12.68141
1997	12.62999
1998	12.40811
1999	12.30762
2000	11.96365
2001	11.77876
2002	11.72299
2003	11.73991
2004	11.62293
2005	11.5366
2006	11.60191
2007	11.38974
2008	11.38713
2009	11.40097
2010	11.42377
2011	11.46512
2012	11.55823
2013	11.75595
2014	11.74737
2015	11.73668
2016	11.42687
2017	11.42341
2018	11.42415