Year	Number
1980	5.1491819057
1981	5.1856180393
1982	5.222054173
1983	5.2584903066
1984	5.2949264403
1985	5.3313625739
1986	5.3677987075
1987	5.4042348412
1988	5.4406709748
1989	5.4771071085
1990	5.5135432421
1991	5.5499793758
1992	5.5864155094
1993	5.6228516431
1994	5.6592877767
1995	5.4943564616
1996	5.3294251466
1997	5.1644938315
1998	4.9995625164
1999	4.8346312013
2000	4.6696998863
2001	4.5047685712
2002	4.3398372561
2003	4.174905941
2004	4.009974626
2005	3.8450433109
2006	3.6790182868
2007	3.5129932628
2008	3.5779595765
2009	3.6429258903
2010	4.0011763448
2011	4.3594267993
2012	4.7176772538
2013	5.0759277083
2014	5.4341781628
2015	5.7924286173
2016	6.1506790718
2017	6.5089295263
2018	20.0421348315
2019	21.5688202247
2020	21.6404494382