Year	1=low to 6=high
2005	3.1
2006	3.3
2007	3.3
2008	3.3
2009	3.3
2010	3.4
2011	3.5
2012	3.5
2013	3.4
2014	3.4
2015	3.4
2016	3.4
2017	3.4
2018	3.4
2019	3.5
2020	3.5
2021	3.6
2022	3.8
2023	3.8