Year	Number of
1980	17
1981	1
1982	1
1983	6
1984	4
1985	2
1986	1
1987	2
1988	0
1989	4
1990	0
1991	1
1992	3
1993	0
1994	3
1995	4
1996	0
1997	2
1998	2
1999	5
2000	0
2002	1
2003	2
2004	2
2006	1
2007	3
2008	5
2009	5
2010	4
2011	2
2012	1
2014	0
2015	5
2016	6
2017	3
2018	2
2019	3
2020	1