Year	Number of
1990	15.99
1991	16.62
1992	17.26
1993	17.92
1994	18.62
1995	19.39
1996	20.39
1997	21.46
1998	22.67
1999	23.9
2000	25.15
2001	26.47
2002	27.81
2003	29.3
2004	30.9
2005	32.65
2006	34.38
2007	36.25
2008	38.36
2009	40.61
2010	43
2011	45.15
2012	47.42
2013	49.83
2014	52.4
2015	55.16
2016	57.99