Year	Number of
1990	23.15
1991	22.8
1992	22.48
1993	22.35
1994	22.55
1995	23.15
1996	24.3
1997	26
1998	28.06
1999	30.1
2000	31.94
2001	33.36
2002	34.5
2003	35.48
2004	36.61
2005	38.06
2006	39.8
2007	41.87
2008	44.27
2009	46.8
2010	49.39
2011	51.07
2012	52.7
2013	54.22
2014	55.82
2015	57.57
2016	59.63