Year	Number of
1990	16.09
1991	16.63
1992	17.11
1993	17.52
1994	17.94
1995	18.38
1996	18.54
1997	18.29
1998	18.39
1999	18.4
2000	18.88
2001	20.07
2002	21.38
2003	22.94
2004	24.8
2005	27.26
2006	29.33
2007	31.57
2008	33.66
2009	35.65
2010	37.76
2011	40.86
2012	43.79
2013	46.79
2014	50.35
2015	54.12
2016	57.78