Year	Number of
1990	10.92
1991	11.32
1992	11.76
1993	12.07
1994	12.53
1995	12.87
1996	13.06
1997	13.82
1998	14.28
1999	15.05
2000	15.34
2001	16.17
2002	17.5
2003	18.32
2004	18.58
2005	19.6
2006	20.34
2007	21.09
2008	22.4
2009	23
2010	24.84
2011	26.52
2012	28.09
2013	30.43
2014	31.01
2015	31.91
2016	33.4