Year	Number of
1990	18.04
1991	18.46
1992	19.52
1993	20.71
1994	21.47
1995	21.86
1996	22.54
1997	23.56
1998	24.8
1999	26.37
2000	28.01
2001	29.54
2002	31.15
2003	32.18
2004	33.16
2005	33.92
2006	34.66
2007	35.6
2008	36.62
2009	37.59
2010	38.88
2011	40.15
2012	41.41
2013	42.91
2014	44.37
2015	45.52
2016	46.46