Year	Number
1979	7.921319648601896
1980	6.249891240226877
1981	4.570897172940429
1982	4.5373473664395805
1983	3.5863799609648193
1984	2.562783583139799
1985	3.218766768960391
1986	3.034632682406057
1987	4.137024545316017
1988	4.22486391287684
1989	5.111283698194798
1991	3.583060839564062
1992	4.18598735804432
1993	4.988205533972804
1994	5.401403167116373
1995	3.744357805550065
1996	3.458945538838716
1997	3.24508639567417
1998	3.511206508809044
1999	3.4396025018381478
2000	3.485704590480321
2004	4.35046887152276
2005	4.8301370114796605
2006	5.201562887533772
2007	5.1286985202028195
2008	4.795566994314317
2009	5.968407028724115
2010	5.735699985195787
2011	5.367156116519789
2012	5.518788303975834
2013	5.5482587176764255
2014	5.110451176790163
2015	6.1580771984993845
2016	7.140085013436294
2017	6.462944957895479
2018	5.75487079401751
2019	6.411070561582803
2020	9.038219535316523
2021	6.194031945555002
2022	4.752665910474819
2023	5.480000906263538