Year	Number
1977	3.674361214411802
1978	2.6289104321807475
1979	4.783966476964639
1980	4.9316732252396935
1981	2.577604184224732
1982	2.761579608647892
1983	3.1572348417774068
1984	2.507077687500514
1985	2.8362542924686274
1986	3.0396781957792887
1987	2.9564572364929607
1988	2.8884787522574884
1989	3.3094291246267615
1990	3.362842230070831
1991	3.328431110890423
1992	2.873027003659351
1993	3.424035855035339
1994	3.8714414349182853
1995	3.293549500579434
1996	4.96228563204305
1997	7.601355253504617
1998	8.075117841892297
1999	3.4485763786084944
2000	4.856290924715764
2001	4.681782002745292
2002	4.922194824702805
2003	5.12322069690976
2004	5.648635257942968
2005	8.329412712942167
2006	8.741928664326283
2007	7.659956358911946
2008	6.32042488371701
2009	7.0308487335241
2010	5.920762844529526
2011	4.397028262644557
2012	4.732554501336142
2013	5.944943607177853
2014	5.984827779949601
2015	6.7320146796091125
2016	7.523941653349957
2017	7.546054193699901
2018	6.0990047920416455
2019	6.024070521443569
2020	8.626276277714448
2021	6.7194809988323305
2022	5.640918897522761
2023	6.155311399307704