Year	Number
1975	12.50753
1976	12.4342
1977	12.34745
1978	12.26081
1979	12.23794
1980	12.21738
1981	12.34729
1982	12.0576
1983	11.78438
1984	11.50756
1985	11.25827
1986	10.96089
1987	10.89944
1988	10.81956
1989	11.04085
1990	10.92423
1991	10.43182
1992	10.12285
1993	10.32154
1994	9.75877
1995	9.70898
1996	9.66197
1997	9.61202
1998	9.56924
1999	9.62676
2000	9.70528
2001	9.80165
2002	9.94162
2003	10.18283
2004	10.20845
2005	10.29895
2006	10.418
2007	10.46019
2008	10.4201
2009	10.44876
2010	10.48084
2011	10.55224
2012	10.57591
2013	10.44051
2014	10.37295
2015	10.38468
2016	10.34085
2017	10.36657
2018	10.3576