Year	Number
1970	39.90121
1971	40.05364
1972	40.18526
1973	40.01123
1974	40.36181
1975	40.60133
1976	40.74933
1977	40.85028
1978	40.23612
1979	39.90235
1980	40.64748
1981	40.95266
1982	40.19454
1983	39.4291
1984	38.81889
1985	38.1688
1986	37.06191
1987	37.17651
1988	37.51758
1989	37.16708
1990	37.56485
1991	38.17838
1992	37.37458
1993	37.67366
1994	39.01453
1995	39.70097
1996	39.84979
1997	42.20567
1998	42.5527
1999	41.61852
2000	43.53539
2001	44.29519
2002	45.32273
2003	45.98481
2004	45.46054
2005	45.2227
2006	44.29735
2007	44.10805
2008	44.00887
2009	43.50385
2010	42.29911
2011	42.12942
2012	41.22102
2013	40.9112
2014	40.48945
2015	39.91367
2016	39.66627
2017	39.64473
2018	39.66142