Year Number 1996 0.187617555260658 1998 0.302315533161163 2000 0.331546425819397 2002 0.259350627660751 2003 0.298997640609741 2004 0.325737655162811 2005 0.224412888288498 2006 0.296224117279053 2007 0.297346860170364 2008 0.296866953372955 2009 0.294009476900101 2010 0.302436739206314 2011 0.296791970729828 2012 0.260998487472534 2013 0.252568811178207 2014 0.28580966591835 2015 0.275554895401001 2016 0.283764690160751 2017 0.293822139501572 2018 0.292914599180222 2019 0.293495029211044 2020 0.305667519569397 2021 0.308144867420197 2022 0.320557087659836