Year	Number
1975	9.9084668192
1976	9.9016018307
1977	9.8947368421
1978	9.8878718535
1979	9.881006865
1980	9.8741418764
1981	9.9176201373
1982	9.9610983982
1983	10.004576659
1984	10.0480549199
1985	10.0915331808
1986	10.1182303585
1987	10.1449275362
1988	10.171624714
1989	10.1983218917
1990	10.2250190694
1991	10.2517162471
1992	10.2784134249
1993	10.1739893211
1994	10.0695652174
1995	9.9651411137
1996	9.8607170099
1997	9.7562929062
1998	9.7257055683
1999	9.6951182304
2000	9.6645308924
2001	9.6339435545
2002	9.6033562166
2003	9.4075133486
2004	9.2116704805
2005	9.0158276125
2006	8.8199847445
2007	8.6241418764
2008	8.4282990084
2009	8.2324561404
2010	8.0366132723
2011	7.8407704043
2012	7.6277650648
2013	6.5598779558
2014	6.4988558352
2015	6.5061670481
2016	6.4988558352
2017	6.4988558352
2018	6.4988558352
2019	6.4988558352
2020	6.4988558352