Year	1=low to 6=high
2005	3.9
2006	3.9
2007	3.9
2008	3.9
2009	3.8
2010	3.9
2011	3.9
2012	3.9
2013	3.9
2014	3.7
2015	3.6
2016	3.6
2017	3.5
2018	3.5
2019	3.7
2020	3.7
2021	3.8
2022	3.8
2023	3.9