Year	Number
1981	14.28646
1984	13.97354
1986	13.66913
1989	13.19464
1991	11.61847
1992	10.93644
1993	10.94796
1994	11.61248
1995	11.91584
1996	10.7619
1998	10.65618
1999	10.3782
2000	10.09735
2001	9.99994
2002	9.84955
2003	9.86682
2004	12.53241
2005	13.58707
2006	13.50326
2007	13.37599
2008	13.25773
2009	12.77748
2010	12.45689
2011	12.3471
2012	12.39973
2013	12.62694
2014	12.56513
2015	12.439
2016	12.21029
2017	11.97279