Year	Number of
1969	52
1970	52
1971	48
1972	41
1973	34
1974	27
1975	23
1976	22
1977	21
1978	22
1979	23
1980	23
1981	22
1982	20
1983	19
1984	17
1985	15
1986	14
1987	12
1988	11
1989	11
1990	11
1991	13
1992	15
1993	17
1994	19
1995	20
1996	20
1997	18
1998	16
1999	13
2000	12
2001	10
2002	10
2003	10
2004	10
2005	11
2006	11
2007	12
2008	13
2009	14
2010	15
2011	16
2012	16
2013	17
2014	17
2015	17