Year	Number of
1990	5.78
1991	6.02
1992	6.29
1993	6.54
1994	6.84
1995	6.92
1996	7.66
1997	8.49
1998	9.45
1999	10.15
2000	11.06
2001	11.53
2002	12.09
2003	12.77
2004	13.62
2005	14.49
2006	15.61
2007	16.63
2008	17.65
2009	18.86
2010	20.18
2011	20.76
2012	21.38
2013	22.12
2014	22.88
2015	23.65
2016	24.37