Year	1=extremely inefficient to 7=extremely efficient
2007	2.58333333333333
2008	2.68039549521073
2009	2.6671355455
2010	2.62111135
2011	2.9
2012	3.2
2013	3.3
2014	3.4
2015	3.47962051858965
2016	3.5
2017	3.8