Year	Number
1971	11.32323
1972	11.0565
1973	11.9573
1974	11.07635
1978	12.66772
1980	12.68894
1981	14.1394
1986	13.44654
1987	12.72174
1988	11.30452
1997	10.15374
1999	11.64506
2000	10.88618
2001	10.75392
2002	10.61697
2003	10.58737
2004	10.48169
2005	10.29087
2006	10.09245
2007	10.1755
2008	10.19668
2010	8.49531
2011	8.62161
2012	7.88117
2013	7.9546
2014	9.11907
2015	9.44748
2016	8.82794