Year	Number of
1990	35.46
1991	35.82
1992	36.19
1993	36.53
1994	36.88
1995	37.51
1996	37.7
1997	38.02
1998	38.56
1999	39.6
2000	40.13
2001	41.1
2002	42.02
2003	43.04
2004	45.31
2005	46.41
2006	47.86
2007	49.48
2008	51.27
2009	53.65
2010	55.97
2011	57.97
2012	59.76
2013	62.09
2014	64.11
2015	66.28
2016	68.32