Year	Number of
1990	20.99
1991	21.63
1992	22.54
1993	23.59
1994	24.61
1995	25.54
1996	25.67
1997	25.68
1998	25.88
1999	26.15
2000	26.63
2001	27.71
2002	28.89
2003	29.86
2004	30.94
2005	32.17
2006	33.45
2007	34.77
2008	36.13
2009	37.61
2010	39.27
2011	40.29
2012	41.33
2013	42.35
2014	43.4
2015	44.51
2016	45.69