Year	Number
1970	37.85643
1971	37.77586
1972	37.8839
1973	37.6868
1974	38.1987
1975	38.33735
1976	38.50424
1977	38.65196
1978	38.27923
1979	38.16029
1980	38.72851
1981	39.2711
1982	38.55447
1983	37.785
1984	37.05013
1985	36.23678
1986	35.4682
1987	35.52555
1988	36.03924
1989	35.88669
1990	35.89419
1991	36.12411
1992	35.45572
1993	35.46944
1994	36.66761
1995	37.4148
1996	37.59193
1997	39.87831
1998	40.17711
1999	39.67975
2000	41.30806
2001	42.01079
2002	44.21167
2003	45.35075
2004	44.89205
2005	45.4124
2006	44.78245
2007	45.17992
2008	45.24996
2009	44.28558
2010	43.14874
2011	42.53344
2012	41.65819
2013	41.48549
2014	40.90913
2015	40.13131
2016	39.76567
2017	39.80427
2018	39.82732