Year	Number of
1990	22.59
1991	23.18
1992	23.83
1993	24.47
1994	25.15
1995	26.01
1996	26.57
1997	27.18
1998	27.85
1999	28.45
2000	28.91
2001	28.75
2002	29.25
2003	29.49
2004	30.29
2005	30.29
2006	31.2
2007	32.15
2008	32.86
2009	34
2010	34.72
2011	35.12
2012	36.18
2013	37.15
2014	38.06
2015	39.1
2016	40.3