Year	Number of
1990	47.2
1991	46.86
1992	47.07
1993	47.19
1994	47.8
1995	47.88
1996	46.78
1997	45.56
1998	44.83
1999	44.02
2000	44.06
2001	44
2002	43.57
2003	43.58
2004	44.02
2005	44.29
2006	45.35
2007	46.74
2008	48.36
2009	50.17
2010	51.99
2011	54.74
2012	57.77
2013	61.15
2014	64.48
2015	68.19
2016	72.13