Year	Number of
1990	17.18
1991	18.17
1992	19.19
1993	20.28
1994	21.45
1995	22.72
1996	23.71
1997	24.78
1998	25.94
1999	27.19
2000	28.54
2001	29.46
2002	30.48
2003	31.57
2004	32.73
2005	33.95
2006	35.45
2007	37.04
2008	38.75
2009	40.58
2010	42.53
2011	44.41
2012	46.41
2013	48.5
2014	50.74
2015	53.12
2016	55.53