Year	Number of
1990	25.8
1991	22.75
1992	20.67
1993	20.65
1994	19.6
1995	18.58
1996	18.76
1997	19.85
1998	20.2
1999	21.3
2000	22.35
2001	22.96
2002	23.81
2003	25.08
2004	26.63
2005	28.48
2006	30.08
2007	32.2
2008	34.61
2009	35.67
2010	35.36
2011	35.44
2012	35.2
2013	34.99
2014	37.32
2015	40.76
2016	43.63