Year	Number
1970	11800
1971	11500
1972	11900
1973	11500
1974	11400
1975	14600
1976	13800
1977	14800
1978	16400
1979	17800
1980	18500
1981	16700
1982	15000
1983	15500
1984	14900
1985	15400
1986	17400
1987	15300
1988	15900
1989	16100
1990	15600
1991	15100
1992	14000
1993	12600
1994	15300
1995	16600
1996	31700
1997	34700
1998	32000
1999	24000
2000	21566
2001	20007
2002	20560
2003	28901
2004	25764
2005	25644
2006	21978
2007	24089
2008	21088
2009	19011
2010	37019
2011	40751.4507216495
2012	41974.6792042443
2013	33467
2014	51017.0018723656
2015	42682
2016	45722
2017	54102
2018	56592
2019	49931
2020	31354
2021	45832.196