Year	Number
1971	11.51306
1972	11.322
1973	13.37235
1976	11.26253
1977	10.95365
1978	10.81326
1979	10.67915
1980	10.37101
1981	10.22482
1982	10.0519
1983	9.99492
1984	9.97182
1985	9.75738
1986	9.53685
1987	9.36358
1988	9.23947
1989	9.07125
1990	9.17612
1991	8.67948
1992	8.48237
1993	8.43933
1994	8.17857
1995	9.55936
1996	10.1963
1998	10.295
1999	10.5428
2000	10.45422
2001	10.13982
2002	10.24765
2003	10.57577
2004	10.80444
2005	10.54004
2006	10.617
2007	10.10115
2013	11.37547
2015	11.29297
2016	10.04517
2017	9.98461