Year	Number of
1990	15.63
1991	14.93
1992	14.24
1993	13.59
1994	13.33
1995	13.08
1996	13.6
1997	14.38
1998	15.35
1999	16.48
2000	17.86
2001	19.02
2002	20.24
2003	20.75
2004	21.84
2005	22.9
2006	24.31
2007	25.98
2008	27.92
2009	29.92
2010	31.92
2011	33.55
2012	35.23
2013	36.94
2014	38.53
2015	40.31
2016	42.21