Year	Number
1980	11.60901
1981	11.7312
1982	11.55622
1983	11.35359
1984	11.1426
1985	10.8767
1986	10.56077
1987	10.48047
1988	10.43474
1989	10.7045
1990	10.68081
1991	10.22534
1992	9.91709
1993	10.09665
1994	9.49917
1995	9.46868
1996	9.40659
1997	9.33031
1998	9.26012
1999	9.31767
2000	9.41639
2001	9.55366
2002	9.60281
2003	9.77989
2004	9.78568
2005	9.85086
2006	9.98294
2007	10.01875
2008	10.0136
2009	10.04528
2010	10.06634
2011	10.23181
2012	10.22815
2013	10.07573
2014	10.00229
2015	10.05194