Year	Number
1973	6.156269685067389
1974	3.366166078139196
1975	2.253918423156216
1976	2.14056955818535
1977	4.452823523428503
1978	4.819183309349873
1979	2.764609215285204
1980	2.695121509408019
1981	2.282945156255896
1982	3.540329676265282
1983	4.152295534474637
1984	5.028791497888673
1985	3.9145484406769993
1986	3.8450990545745145
1987	2.922508791045636
1988	3.322070156721847
1989	3.6037749795342022
1990	3.2310562155426155
1991	3.205294377439648
1992	3.167919949307328
1993	2.905011360099482
1994	2.8876842928252016
1995	2.8493313107424196
1996	2.8362890628109665
1997	3.0018870488668763
1998	2.8904649497676145
1999	2.778356920606752
2000	2.536228728464291
2001	2.9573701397352083
2002	3.034570630075769
2003	3.5570481566234577
2004	3.5838632956115304
2005	4.129415678675744
2006	3.8735097825315705
2007	1.9585145672059932
2008	5.788103458991532
2009	7.595427334903275
2010	6.427220856417171
2011	5.941109528230305
2012	4.918795723640262
2013	4.163717684871909
2014	3.9075523792869715
2015	3.440500575931517
2016	3.907727892305954
2017	3.6432549649403905
2018	3.580566247685389
2019	3.5511167468047637
2020	3.773289582311734
2021	3.245981873555287
2022	3.3509783056068954
2023	2.9075873249690285