Year	Number
1970	14.13402
1971	14.14939
1972	14.08626
1973	14.40006
1974	14.26873
1975	14.11159
1976	13.96361
1977	13.8566
1978	13.84076
1979	13.72527
1980	13.62764
1981	13.55753
1982	13.4967
1983	13.45515
1984	13.40387
1985	13.31817
1986	13.33375
1987	13.25333
1988	13.12371
1989	13.04593
1990	12.74245
1991	12.45698
1992	12.33179
1993	12.20249
1994	12.2521
1995	12.34869
1996	12.21104
1997	12.21568
1998	12.40997
1999	12.54052
2000	12.32525
2001	12.22444
2002	12.24924
2003	12.30227
2004	12.03165
2005	11.81862
2006	11.78432
2007	11.58689
2008	11.60798
2009	11.60223
2010	11.62734
2011	11.52783
2012	11.57438
2013	12.00959
2014	12.0173
2015	11.91926
2016	11.73981
2017	11.7795
2018	11.79284