Year	Number of
1990	17.93
1991	17.19
1992	16.75
1993	17.61
1994	16.92
1995	16.14
1996	17.59
1997	19.04
1998	21.19
1999	21.8
2000	23.36
2001	25.57
2002	25.6
2003	27.53
2004	30.26
2005	33.59
2006	36.41
2007	38.19
2008	42
2009	43.51
2010	44.48
2011	46.7
2012	48.13
2013	51.85
2014	53.99
2015	56.89
2016	61.5