Year	Number
1970	13.3382
1971	13.55506
1972	13.83136
1973	14.25333
1974	14.55326
1975	14.89438
1976	15.07845
1977	15.10078
1978	15.301
1979	15.23993
1980	15.4875
1981	15.61047
1982	15.72416
1983	15.82128
1984	15.89084
1985	15.84628
1986	15.93238
1987	15.88637
1988	15.9377
1989	16.04023
1990	16.12256
1991	16.27462
1992	16.44044
1993	16.61881
1994	16.74029
1995	17.01382
1996	17.08467
1997	17.28014
1998	17.41988
1999	17.46206
2000	17.74447
2001	18.438
2002	18.44658
2003	17.28664
2004	17.15479
2005	16.86362
2006	17.60748
2007	18.1657
2008	17.47938
2009	17.49306
2010	17.26036
2011	17.06215
2012	16.89054
2013	17.30006
2014	16.57641
2015	16.49783
2016	16.53588
2017	16.61526
2018	16.60104