Year	1=low to 6=high
2005	3.3
2006	3.4
2007	3.5
2008	3.5
2009	3.5
2010	3.7
2011	3.6
2012	3.6
2013	3.6
2014	3.6
2015	3.7
2016	3.7
2017	3.7
2018	3.8
2019	3.8
2020	3.8
2021	3.8
2022	3.8
2023	3.9