Year	Number
1974	11.35205
1975	13.99099
1977	12.07233
1979	10.48583
1980	9.4354
1981	9.74766
1983	13.10359
1996	8.04391
1998	7.39088
1999	7.81461
2000	8.0121
2001	8.59284
2002	8.12892
2003	8.43045
2004	8.14447
2005	9.31057
2006	7.8889
2007	8.00082
2008	7.40422
2009	8.65
2010	7.99553
2011	6.78959
2012	6.4672
2013	7.51274
2014	6.88969
2015	7.60159
2016	7.20777
2017	7.24214