Year 1=extremely inefficient to 7=extremely efficient 2007 4.14071785299223 2008 4.332139506025 2009 4.58481886707143 2010 4.5948058354 2011 4.475 2012 4.32777777777778 2013 4.31578947368421 2014 4.27777777777778 2015 4.32659866410087 2016 4.31764705882353 2017 4.45294117647059