Year	Number of
1990	21.64
1991	22.62
1992	23.8
1993	25.06
1994	26.43
1995	27.96
1996	29.07
1997	30.25
1998	31.5
1999	32.85
2000	34.35
2001	34.4
2002	34.52
2003	34.7
2004	34.93
2005	35.21
2006	35.89
2007	36.58
2008	37.32
2009	38.11
2010	38.97
2011	39.97
2012	41.04
2013	42.16
2014	43.34
2015	44.57
2016	47.61