Year	years
2003	2.9740740740740748
2004	2.946987951807229
2005	2.9634408602150546
2006	2.9484210526315793
2007	2.9385416666666675
2008	2.9385416666666675
2009	2.9288659793814436
2010	2.904123711340206
2011	2.849484536082474
2012	2.837755102040817
2013	2.767924528301887
2014	2.7594339622641515
2015	2.766037735849057
2016	2.7443396226415104
2017	2.7490566037735857
2018	2.7490566037735853
2019	2.716037735849057