Year	Number of
1990	14.29
1991	14.84
1992	15.24
1993	16.17
1994	16.85
1995	17.74
1996	18.48
1997	18.87
1998	19.29
1999	19.91
2000	20.53
2001	21.2
2002	22.27
2003	23.98
2004	26.32
2005	27.88
2006	28.43
2007	28.84
2008	30.44
2009	32.98
2010	35.26
2011	37.04
2012	38.84
2013	40.08
2014	41.5
2015	42.92
2016	44.43