Year	Number of
1968	28610
1969	29060
1970	29460
1971	29720
1972	30060
1973	30700
1974	31420
1975	32300
1976	33380
1977	34590
1978	35660
1979	36680
1980	37700
1981	38630
1982	39490
1983	40200
1984	40650
1985	41130
1986	41470
1987	41820
1988	42100
1989	42520
1990	42980
1991	43340
1992	43760
1993	44250
1994	44460
1995	44580
1996	44440
1997	44120
1998	43650
1999	43230
2000	42850
2001	42640
2002	42620
2003	42630
2004	42610
2005	42290
2006	41630
2007	40580
2008	39760
2009	38970
2010	38420
2011	38370
2012	38400
2013	38610
2014	38680
2015	38580