Year	Number of
1990	30.3
1991	29.86
1992	29.39
1993	28.91
1994	28.51
1995	28.2
1996	25.95
1997	23.93
1998	22.09
1999	20.41
2000	18.89
2001	18.52
2002	18.19
2003	17.9
2004	17.63
2005	17.39
2006	18.31
2007	19.29
2008	20.36
2009	21.51
2010	22.76
2011	23.6
2012	24.49
2013	25.4
2014	26.36
2015	27.36
2016	28.46