Year	Number of
1990	10.62
1991	11.92
1992	13.39
1993	13.32
1994	14.43
1995	14.09
1996	13.44
1997	12.45
1998	13.42
1999	13.9
2000	16.56
2001	18.13
2002	18.19
2003	18.98
2004	20.51
2005	21.38
2006	21.97
2007	22.38
2008	23.11
2009	22.81
2010	22.09
2011	21.69
2012	21.53
2013	22.3
2014	23.01
2015	23.83
2016	24.64