Year Percent 2005 2.69436 2006 2.31281 2007 1.74974 2008 1.88294 2009 1.85179 2010 1.81435 2011 1.74897 2012 1.65646 2013 1.45226 2014 1.47227 2015 1.41525 2016 1.47917 2017 1.6671