Year	Number of
1990	19.91
1991	20.39
1992	20.9
1993	21.48
1994	22.15
1995	22.71
1996	23.4
1997	24.43
1998	25.32
1999	26.27
2000	26.67
2001	27.7
2002	28.72
2003	29.86
2004	31
2005	32.31
2006	33.7
2007	35.31
2008	36.77
2009	38.19
2010	39.4
2011	40.32
2012	41.29
2013	42.33
2014	43.46
2015	44.77
2016	46.08