Year	Number of
1990	23.27
1991	23.79
1992	24.12
1993	25.06
1994	26.03
1995	26.93
1996	28.64
1997	28.33
1998	28.76
1999	29.53
2000	30.1
2001	30.01
2002	29.7
2003	30.61
2004	31.09
2005	32.26
2006	34.3
2007	35.32
2008	36.19
2009	37.65
2010	37.97
2011	37.83
2012	37.97
2013	38.5
2014	40.05
2015	41.43
2016	43.04