Year	Number of
1990	22.37
1991	22.86
1992	23.76
1993	24.73
1994	25.61
1995	26.38
1996	26.79
1997	27.02
1998	27.36
1999	27.62
2000	27.86
2001	28.73
2002	29.65
2003	30.52
2004	31.48
2005	32.59
2006	33.73
2007	34.93
2008	36.11
2009	37.41
2010	38.92
2011	40.44
2012	42.03
2013	43.59
2014	45.12
2015	46.63
2016	48.23