Year	Overall average
2004	51.077441010101
2005	52.2558922222222
2006	52.9084966666667
2007	53.8888888235294
2008	53.3986928431372
2009	54.2483661764706
2010	56.4052289215686
2011	57.2549018627451
2012	56.8571425714286
2013	56.8981481481482
2014	56.3425925925926
2015	57.8086546296296
2016	58.3024805555556
2017	58.2407472222222
2018	59.8456888888889