Year	Number
1971	14.67389
1972	11.8173
1973	12.98574
1974	12.44376
1975	13.03326
1976	12.97398
1977	12.27604
1979	11.91707
1980	12.41498
1981	11.91079
1982	12.24771
1983	12.09809
1984	13.73081
1985	12.82123
1986	11.99957
1987	11.80424
1988	11.74796
1989	12.04065
1990	12.22619
1991	12.10714
1992	12.85372
1993	12.77454
1994	11.69455
1995	11.33238
1996	11.53522
1997	11.52503
1998	11.24551
1999	10.89978
2000	10.70128
2001	10.40219
2002	10.50319
2003	10.09776
2004	11.59322
2005	11.46871
2006	11.30159
2007	10.84173
2008	10.64056
2011	8.3145
2012	8.52146
2013	8.09958
2014	7.87035
2015	7.79572
2016	7.21022
2017	7.11247