Year	Number of
1990	22.05
1991	23.08
1992	24.1
1993	25.02
1994	25.77
1995	26.39
1996	25.49
1997	24.35
1998	23.46
1999	22.64
2000	22.12
2001	22.93
2002	24.23
2003	26
2004	27.5
2005	28.7
2006	30.51
2007	32.33
2008	34.23
2009	36.43
2010	38.81
2011	39.89
2012	40.85
2013	41.63
2014	42.52
2015	43.57
2016	44.34