Year	Number
2001	2.0191905539655846
2002	1.8877693259813026
2003	1.6463808013121934
2004	1.4566903258045465
2005	1.3991755055512358
2006	1.226022069362681
2007	1.1665503168566467
2008	1.5392873739404833
2009	1.3719387441474067
2010	1.6368259561756133
2011	1.9490763542239509
2012	1.9417205826768367
2013	2.302851893416987
2014	2.8949371827444206
2015	2.2904784269455827
2016	2.0129738433202897
2017	2.1653158050637504
2018	2.0906856749916827
2019	1.7955946543123291
2020	1.7495871932043114