Year	1=low to 6=high
2005	3.1
2006	3.2
2007	3.2
2008	3.2
2009	3.5
2010	3.7
2011	3.7
2012	3.7
2013	3.7
2014	3.7
2015	3.7
2016	3.7
2017	3.7
2018	3.7
2019	3.7
2020	3.7
2021	3.8
2022	3.8
2023	3.9