Year	Number of
1990	20.7
1991	21.17
1992	21.08
1993	21.8
1994	22.52
1995	22.66
1996	22.51
1997	23.5
1998	25.94
1999	27.46
2000	28.71
2001	30.5
2002	32.76
2003	34.59
2004	35.42
2005	36.51
2006	36.32
2007	36.93
2008	37.91
2009	38.97
2010	38.99
2011	39.8
2012	41.04
2013	42.62
2014	43.32
2015	45.56
2016	47.51