Year	Number
1981	2.9180398759899147
1982	2.048188028225795
1983	2.235383787783634
1984	2.8442454542864017
1985	3.2447400749800632
1986	3.1365041095878463
1987	4.018485597834597
1988	3.2952881804919802
1989	2.9932704301169037
1990	3.1374664531085292
1991	3.2799205228735278
1992	3.3316624198059674
1993	3.3837906830497007
1994	3.2307371158706357
1995	2.902138290927532
1996	3.494959046327402
1997	2.9548079433766845
1998	5.233226029982246
1999	6.092294500729943
2000	5.264836072413461
2001	5.669053783405978
2002	6.295267965763302
2003	6.774904410930198
2004	5.420563210953007
2005	4.104784855177618
2006	4.91547534687068
2007	5.6771252973221955
2008	4.0009626453168385
2009	6.5468457568991445
2010	6.8699143299107375
2011	6.059690449406221
2012	5.58937942738163
2013	4.950318467695986
2014	5.744323399472589
2015	6.446161057664064
2016	7.225888056095326
2017	7.087162420111019
2018	5.595607588484021
2019	6.317774344194999
2020	8.406974846397976
2021	6.785175853930198
2022	5.213220774700963
2023	5.70417964320922