Year	Number
1971	10.90625
1972	10
1973	9.11881
1974	7.38261
1978	8.24812
1979	7.99451
1980	7.42439
1981	8.54626
1982	8.00405
1983	7.07451
1984	8.12177
1985	8.89655
1986	9.13703
1987	9.04497
1988	9.67426
1989	11.7814
1990	12.16632
1991	9.52616
1992	12.16082
1993	8.94714
1994	9.28552
1995	9.52761
1996	9.62473
1997	9.40811
1999	10.04819
2000	9.62477
2001	10.52381
2002	12.19527
2003	13.68689
2004	14.28014
2005	13.83735
2006	11.94835
2007	12.18586
2008	10.98247
2009	13.09637
2010	12.62554
2011	12.03372
2012	11.72399
2013	11.33913
2014	12.68324
2015	12.65441
2016	12.25608
2017	13.91423