Year	Number of
1990	6.82
1991	6.57
1992	6.36
1993	6.23
1994	6.5
1995	7.18
1996	8.33
1997	7.72
1998	10.48
1999	12.05
2000	13.73
2001	14.38
2002	13.69
2003	13.29
2004	12.03
2005	12.25
2006	13.81
2007	16.38
2008	17.08
2009	18.31
2010	18.66
2011	18.09
2012	18.86
2013	18.51
2014	18.9
2015	21.51
2016	23.92