Year	Number of
1990	16.51
1991	17.3
1992	18.07
1993	18.82
1994	19.59
1995	20.42
1996	21.21
1997	22.04
1998	22.91
1999	23.83
2000	24.83
2001	25.82
2002	26.87
2003	28
2004	29.2
2005	30.49
2006	31.83
2007	33.27
2008	34.85
2009	36.54
2010	38.34
2011	40.07
2012	41.92
2013	43.87
2014	45.91
2015	48.05
2016	50.23