Year	Number
1988	2.133105802
1989	2.2544669745
1990	2.375828147
1991	2.4971893194
1992	2.6185504919
1993	2.7399116643
1994	2.8612728368
1995	2.9826340092
1996	3.1039951817
1997	3.2253563541
1998	3.3467175266
1999	3.4680786991
2000	3.5894398715
2001	3.710801044
2002	3.8321622164
2003	3.9535233889
2004	4.0748845613
2005	4.1962457338
2006	4.4464827455
2007	4.6967197573
2008	4.9469567691
2009	5.1971937808
2010	5.4474307926
2011	5.6976678043
2012	5.9479048161
2013	6.1981418278
2014	6.4483788396
2015	7.3442832765
2016	7.4539249147
2017	6.7461134812
2018	10.3733404437
2019	11.0209377133
2020	11.0209377133