Year	Number of
1990	11.34
1991	12.28
1992	13.33
1993	14.49
1994	15.77
1995	17.14
1996	17.73
1997	18.36
1998	19.1
1999	19.96
2000	20.97
2001	21.61
2002	22.43
2003	23.56
2004	25.09
2005	27.13
2006	29.17
2007	31.8
2008	34.84
2009	37.91
2010	40.75
2011	44.03
2012	46.75
2013	49.03
2014	51.16
2015	53.39
2016	57.05