Year	Number of
1990	21.66
1991	22.31
1992	22.95
1993	23.76
1994	24.73
1995	25.93
1996	27.33
1997	29.22
1998	29.94
1999	31.7
2000	34.37
2001	36.75
2002	40.26
2003	43.29
2004	45.27
2005	47.2
2006	48.89
2007	50.41
2008	53.68
2009	57.28
2010	61.37
2011	65.48
2012	68.63
2013	72.24
2014	77.79
2015	81.58
2016	85.69