Year	Number of
1990	24.17
1991	24.98
1992	25.83
1993	26.74
1994	27.69
1995	28.73
1996	30.1
1997	31.57
1998	33.19
1999	35.05
2000	36.98
2001	37.87
2002	38.75
2003	39.59
2004	40.42
2005	41.26
2006	41.53
2007	41.97
2008	42.51
2009	43.01
2010	43.67
2011	44.57
2012	45.63
2013	46.73
2014	47.98
2015	49.29
2016	50.58