Year	Number of
1981	17
1982	17.42
1983	21.72
1984	20.67
1985	18.42
1986	13.49
1987	19.34
1988	21.21
1989	20.16
1990	24.29
1992	25.82
1993	24.92
1995	16.08
1996	18.43
1997	18.19
1998	16.24
1999	16.98
2001	18.05
2002	15.91
2003	17.48
2004	14.98
2005	13.37
2006	11.16
2007	11.1
2008	9.339
2009	9.133
2011	8.921
2012	7.45