Year	Number
1981	11.71491
1986	11.20584
1989	9.87114
1990	9.59315
1991	9.18539
1992	9.02172
1993	8.38491
1994	8.54856
1995	8.56808
1996	8.41612
1997	8.01682
1998	9.89391
1999	10.27731
2000	10.73766
2001	11.24387
2002	11.36004
2003	11.14677
2004	11.02829
2005	10.81161
2006	10.25442
2008	9.84145
2009	8.60649
2010	9
2011	8.33016
2012	7.89986
2013	8.32843
2014	8.21486
2015	8.03226
2016	8.10571
2017	8.2712