Year	Number of
1990	38.3
1991	37.8
1992	37.36
1993	37.03
1994	36.72
1995	36.44
1996	37.33
1997	38.27
1998	39.32
1999	40.43
2000	41.63
2001	43.3
2002	45.1
2003	47.09
2004	49.18
2005	51.38
2006	54.21
2007	57.16
2008	60.38
2009	63.83
2010	67.56
2011	70.53
2012	73.72
2013	77.16
2014	80.78
2015	84.59
2016	88.6