Year	Number of
1990	20.55
1991	21.13
1992	21.6
1993	22.14
1994	22.6
1995	23.21
1996	23.26
1997	22.77
1998	23.26
1999	23.46
2000	23.19
2001	23.65
2002	25.13
2003	26.66
2004	28.41
2005	29.48
2006	30.83
2007	32.35
2008	33.65
2009	35.29
2010	36.78
2011	38.05
2012	39.52
2013	40.97
2014	42.53
2015	44.14
2016	45.55