Year	Number
1981	12.28149
1982	12.53388
1983	12.52492
1984	12.48901
1985	12.41173
1986	12.08037
1987	11.90998
1988	12.07742
1989	11.88831
1990	11.57944
1991	11.32799
1992	10.12475
1993	11.13392
1994	11.54695
1995	11.17172
1996	10.96733
1997	11.00772
1998	10.2427
1999	10.89747
2000	11.03544
2001	10.63347
2002	10.41181
2003	10.04037
2004	9.36212
2005	9.39089
2006	9.21824
2007	9.16603
2008	9.18833
2009	9.17091
2010	9.23715
2011	9.16371
2012	9.15306
2013	9.18952
2014	9.15729
2015	9.09206
2016	9.1063