Year	Number of
1990	21.69
1991	22.11
1992	22.58
1993	23.09
1994	23.64
1995	24.25
1996	24.47
1997	24.75
1998	25.08
1999	25.46
2000	25.91
2001	26.55
2002	27.26
2003	28.03
2004	28.85
2005	29.74
2006	30.82
2007	31.93
2008	33.13
2009	34.41
2010	35.83
2011	37.53
2012	39.4
2013	41.36
2014	43.48
2015	45.78
2016	48.31