Year	Number of
1990	28.37
1991	27.03
1992	25.55
1993	24.49
1994	23.98
1995	23.79
1996	24.93
1997	26.11
1998	27.95
1999	29.75
2000	32.04
2001	33.48
2002	35.18
2003	36.17
2004	37.15
2005	38.53
2006	40.79
2007	43.48
2008	46.01
2009	48.92
2010	51.96
2011	54.44
2012	56.23
2013	58.35
2014	60.19
2015	62.15
2016	64.17