Year	Number of
1990	29.1
1991	30.06
1992	31.14
1993	32.03
1994	33.2
1995	34.55
1996	35.81
1997	36.74
1998	37.81
1999	39.76
2000	41.43
2001	42.63
2002	43.21
2003	47.91
2004	51.65
2005	54.87
2006	57.95
2007	60.28
2008	62.75
2009	68.96
2010	69.7
2011	71.17
2012	72.49
2013	74.28
2014	76.43
2015	78.52
2016	81.2