Year	Number of
1990	21.41
1991	21.86
1992	21.76
1993	22.52
1994	23.25
1995	23.35
1996	23.12
1997	24.08
1998	26.6
1999	28.31
2000	29.63
2001	31.61
2002	34.12
2003	36.14
2004	37.12
2005	38.16
2006	37.74
2007	38.03
2008	38.71
2009	39.56
2010	39.43
2011	40.12
2012	41.27
2013	42.81
2014	43.49
2015	45.43
2016	47.07