Year	Number
1980	17.4634516803
1981	17.5207898234
1982	17.5781279666
1983	17.6354661097
1984	17.6928042529
1985	17.7501423961
1986	17.231441048
1987	16.7127397
1988	16.194038352
1989	15.675337004
1990	15.156635656
1991	15.156635656
1992	14.5961647997
1993	14.0356939434
1994	13.4752230871
1995	12.9147522309
1996	12.3542813746
1997	13.2684640213
1998	14.1826466679
1999	15.0968293146
2000	16.0110119613
2001	16.9251946079
2002	18.1765236377
2003	19.4278526676
2004	20.6791816974
2005	21.9305107272
2006	21.3521928992
2007	20.7708372888
2008	20.3341560661
2009	21.6631858743
2010	20.7518511487
2011	19.34687678
2012	20.3531422062
2013	20.2012530852
2014	18.0178469717
2015	15.969242453
2016	15.233339662
2017	15.02980824
2018	16.3669836132
2019	17.0006069189
2020	16.8035605907