Year	Number of
1990	20.88
1991	21.92
1992	22.44
1993	22.54
1994	22.38
1995	22.1
1996	22.38
1997	23.03
1998	24.07
1999	25.23
2000	26.39
2001	27.6
2002	28.8
2003	30.1
2004	31.4
2005	32.78
2006	33.29
2007	33.92
2008	34.79
2009	35.84
2010	37.06
2011	38.61
2012	40.42
2013	42.3
2014	44.24
2015	46.16
2016	48.65