Year	Number of
1990	23.49
1991	24.12
1992	24.76
1993	25.38
1994	26.01
1995	26.82
1996	27.28
1997	27.78
1998	28.31
1999	29.07
2000	29.38
2001	29.98
2002	30.55
2003	31.09
2004	32.79
2005	33.52
2006	34.35
2007	35.33
2008	36.41
2009	37.9
2010	39.34
2011	40.84
2012	42.15
2013	43.85
2014	45.38
2015	47.03
2016	48.6