Year	1=low to 6=high
2005	3.2
2006	3.3
2007	3.4
2008	3.4
2009	3.7
2010	3.7
2011	3.9
2012	3.9
2013	3.9
2014	3.8
2015	3.8
2016	3.8
2017	3.8
2018	3.7
2019	3.7
2020	3.7
2021	3.6
2022	3.6
2023	3.5