Year	Number
1981	12.66667
1982	12.75281
1983	12.87822
1984	12.81209
1985	12.54236
1986	12.13034
1987	11.48427
1988	10.93753
1989	10.30032
1990	10.01143
1991	9.56761
1992	9.46483
1993	9.01975
1994	8.4233
1995	8.8897
1996	8.69672
1997	8.35536
1998	9.99458
1999	10.29757
2000	10.73662
2001	11.39977
2002	11.61168
2003	11.329
2004	11.17149
2005	10.58531
2006	9.96154
2008	8.75846
2009	7.80841
2010	8.35331
2011	7.73197
2012	7.26532
2013	7.37622
2014	7.21192
2015	7.25843
2016	7.34756
2017	7.47934