Year	Number
1960	13775
1961	14363
1962	14657
1963	14822
1964	14958
1965	14864
1966	14567
1967	14242
1968	13806
1969	13265
1970	12583
1971	11792
1972	11383
1973	11264
1974	11343
1975	11464
1976	11682
1977	11946
1978	12102
1979	12204
1980	11846
1981	11151
1982	10219
1983	9020
1984	7471
1985	5557
1986	3133
1987	315
1988	-3045
1989	-6923
1990	-10252
1991	-13008
1992	-15314
1993	-17257
1994	-18818
1995	-20017
1996	-20842
1997	-21349
1998	-21441
1999	-21131
2000	-20514
2001	-19909
2002	-19291
2003	-18671
2004	-18142
2005	-17620
2006	-17116
2007	-16590
2008	-15933
2009	-15152
2010	-14321
2011	-13447
2012	-12981
2013	-12505
2014	-11830
2015	-11163
2016	-10340
2017	-9498
2018	-8632
2019	-7903
2020	-7381
2021	-6815
2022	-8466
2023	-7630