Year	Number
1972	9.21043
1974	12.03097
1975	13.33372
1976	11.82554
1977	13.20374
1978	9.4553
1979	14.10112
1980	11.52754
1981	11.97462
1982	12.03366
1983	12.14491
1984	11.14946
1986	11.18293
1987	10.54379
1988	10.89614
1989	10.19562
1990	9.87485
1991	9.7515
1994	9.31669
1995	9.30656
1996	9.35558
1997	9.46474
1999	9.55211
2000	9.73912
2001	9.813
2002	9.76813
2003	9.65974
2004	9.62867
2005	9.49186
2006	9.34261
2007	9.20793
2008	9.17396
2009	9.28763
2010	9.18651
2011	9.13675
2012	9.236
2013	9.05095
2014	9.79227
2015	9.6658
2017	11.43611