Year	Number of
1990	20.53
1991	21.29
1992	22.47
1993	23.83
1994	25.84
1995	28.08
1996	30.36
1997	32.62
1998	35.03
1999	36.75
2000	38.65
2001	39.88
2002	41
2003	40.96
2004	40.62
2005	39.91
2006	39.77
2007	39.61
2008	40.11
2009	40.21
2010	40.37
2011	40.33
2012	40.74
2013	41.24
2014	41.23
2015	41.88
2016	42.85