Year	Number of
1990	21.13
1991	21.42
1992	21.77
1993	22.17
1994	22.61
1995	23.1
1996	23.27
1997	23.47
1998	23.8
1999	24.48
2000	25.22
2001	25.46
2002	25.74
2003	26.1
2004	26.53
2005	27.01
2006	28.01
2007	29.02
2008	30.06
2009	31.13
2010	32.31
2011	33.69
2012	35.18
2013	36.75
2014	38.46
2015	40.3
2016	42.15