Year	Number
1980	20.9949435083
1981	21.2237770857
1982	21.452610663
1983	21.6814442403
1984	21.9102778177
1985	22.139111395
1986	22.3679449723
1987	22.5967785497
1988	22.825612127
1989	23.0544457043
1990	23.2832792817
1991	23.512112859
1992	23.7409464363
1993	23.9697800137
1994	24.198613591
1995	24.4274471683
1996	24.6562807457
1997	24.885114323
1998	25.1139479003
1999	25.3427814777
2000	25.571615055
2001	25.8004486323
2002	27.1205005477
2003	28.020766126
2004	28.2083214548
2005	28.5834321125
2006	28.8835206386
2007	29.5024532237
2008	29.9266658664
2009	28.7484808018
2010	29.8700616682
2011	29.8137950695
2012	31.0329047069
2013	30.6277851966
2014	31.8581481537
2015	32.1319789338
2016	32.4759554068
2017	32.9497201674
2018	44.4626841768
2019	44.7184296925
2020	44.8170243434