Year	Number of
1990	18.49
1991	19.26
1992	20.08
1993	21.01
1994	21.97
1995	22.97
1996	24.9
1997	26.97
1998	29.32
1999	31.81
2000	34.48
2001	35.42
2002	36.35
2003	37.31
2004	38.37
2005	39.58
2006	39.67
2007	39.85
2008	40.12
2009	40.43
2010	40.76
2011	42.75
2012	44.88
2013	47.16
2014	49.6
2015	52.22
2016	55.04