Year	Number
1986	4.3460350154
1987	4.4055818744
1988	4.4651287333
1989	4.5246755922
1990	4.5842224511
1991	4.64376931
1992	4.5844490216
1993	4.5251287333
1994	4.4658084449
1995	4.4064881565
1996	4.3471678682
1997	4.3388006741
1998	4.33043348
1999	4.3220662859
2000	4.3136990918
2001	4.3053318978
2002	4.2969647037
2003	4.2885975096
2004	4.2802303155
2005	4.2718631214
2006	4.2634959273
2007	4.2551287333
2008	4.1253656025
2009	3.9956024717
2010	3.8309629248
2011	3.666323378
2012	3.7528321318
2013	3.8393408857
2014	3.7595262616
2015	3.6797116375
2016	3.7066426365
2017	3.7335736354
2018	3.7335736354
2019	3.7335736354
2020	3.7335736354