Year	Number of
1990	20.85
1991	20.92
1992	21.05
1993	20.72
1994	21.79
1995	22.03
1996	21.27
1997	21.55
1998	21.57
1999	22.2
2000	23.23
2001	23.77
2002	25.39
2003	27.03
2004	29.11
2005	31.36
2006	32.21
2007	33.39
2008	36.55
2009	37.77
2010	39.42
2011	40.64
2012	40.28
2013	41.09
2014	43.79
2015	44.42
2016	45.18