Year	Number
1975	6.174793307895487
1976	4.213465276607584
1977	7.440130624046754
1978	7.0197172618569486
1979	4.310626792807746
1980	6.887751717557644
1981	8.508531906231008
1982	8.313858459398366
1983	8.832344933049868
1984	6.002758587603147
1985	6.226287807711209
1986	4.315352153685591
1987	6.502372684302156
1988	7.0017309496439
1989	7.9244745279658
1990	8.382585858585859
1991	8.172482870085819
1992	5.7952406087798005
1993	8.303713736131314
1994	7.462854573049332
1995	6.8851109855203
1996	8.391846926254635
1997	8.466640441089018
1998	8.301132290234197
1999	8.822740691068681
2000	10.264911588841931
2001	8.58772697733769
2002	8.228986760578884
2003	7.327365270063522
2004	7.364397950612613
2005	7.563752380961527
2006	7.534357988209796
2007	8.319773233182083
2008	8.957365177679536
2009	8.72237130390362
2010	8.184367141576613
2011	7.671460411062562
2012	7.181392239333651
2013	5.821609573818314
2014	4.025477703304126
2015	3.5569463045484415
2016	3.7854771270456262
2017	4.2726835213636845
2018	4.37141662163893
2019	5.123938365746434
2020	5.885918069222483
2021	4.04495044103676
2022	3.9214898687648967
2023	4.462480947261915