Year	Number of
1990	9.86
1991	10.48
1992	11.14
1993	11.83
1994	12.47
1995	12.93
1996	12.93
1997	12.79
1998	12.57
1999	12.25
2000	12.11
2001	12.55
2002	13.28
2003	14.09
2004	15.1
2005	16.08
2006	17.83
2007	19.43
2008	21.27
2009	23.01
2010	24.86
2011	25.9
2012	26.99
2013	27.75
2014	28.57
2015	29.45
2016	29.98