Year	Number of
1990	40.16
1991	40.06
1992	40.08
1993	39.75
1994	39.83
1995	40.29
1996	41.09
1997	42.18
1998	42.82
1999	41.79
2000	41.95
2001	43.23
2002	44.14
2003	44.49
2004	46.28
2005	47.99
2006	49.16
2007	50.65
2008	52.31
2009	53.48
2010	54.43
2011	55.71
2012	56.54
2013	57.29
2014	58.57
2015	60.37
2016	63.87